Device and method for performing handover in wireless communication system

ABSTRACT

The present disclosure relates to a pre-5th-Generation (5G) or 5G communication system to be provided for supporting higher data rates Beyond 4th-Generation (4G) communication system such as Long Term Evolution (LTE). According to embodiments, a method performed by a user equipment (UE) in a wireless communication system, the method comprises: receiving, from a base station, a radio resource control (RRC) reconfiguration message including conditional configuration information, wherein the conditional configuration information includes: identification information for a candidate cell; and a configuration of the candidate cell; and performing one or more operations for a conditional handover based on RRC reconfiguration message.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based on and claims priority under 35 U.S.C. 119 toKorean Patent Application No. 10-2019-0078031, filed on Jun. 28, 2019,in the Korean Intellectual Property Office, the disclosure of which isherein incorporated by reference in its entirety.

BACKGROUND 1. Field

The disclosure generally relates to a wireless communication system and,more particularly, to a device and method for performing a handover in awireless communication system.

2. Description of Related Art

To meet the demand for wireless data traffic having increased sincedeployment of 4th generation (4G) communication systems, efforts havebeen made to develop an improved 5th generation (5G) or pre-5Gcommunication system. Therefore, the 5G or pre-5G communication systemis also called a ‘Beyond 4G Network’ or a ‘Post LTE System’.

The 5G communication system is considered to be implemented in higherfrequency (mmWave) bands, e.g., 60 GHz bands, so as to accomplish higherdata rates. To decrease propagation loss of the radio waves and increasethe transmission distance, the beamforming, massive multiple-inputmultiple-output (MIMO), Full Dimensional MIMO (FD-MIMO), array antenna,an analog beam forming, large scale antenna techniques are discussed in5G communication systems.

In addition, in 5G communication systems, development for system networkimprovement is under way based on advanced small cells, cloud RadioAccess Networks (RANs), ultra-dense networks, device-to-device (D2D)communication, wireless backhaul, moving network, cooperativecommunication, Coordinated Multi-Points (CoMP), reception-endinterference cancellation and the like.

In the 5G system, Hybrid FSK and QAM Modulation (FQAM) and slidingwindow superposition coding (SWSC) as an advanced coding modulation(ACM), and filter bank multi carrier (FBMC), non-orthogonal multipleaccess (NOMA), and sparse code multiple access (SCMA) as an advancedaccess technology have been developed.

A terminal may perform communication via a base station in a wirelesscommunication system. A cell that provides a service to the terminalfrom among cells of the base station may be referred to as a servingcell. However, since the terminal may move, the quality of the servicefrom the serving cell may deteriorate according to the moving of theterminal, and in the case where the quality of the service from theserving cell deteriorates or a channel quality for an adjacent cell isimproved, a handover from the serving cell of the terminal to theadjacent cell may be required.

The above information is presented as background information only toassist with an understanding of the disclosure. No determination hasbeen made, and no assertion is made, as to whether any of the abovemight be applicable as prior art with regard to the disclosure.

SUMMARY

Based on the foregoing discussion, the disclosure provides a device andmethod for performing a handover in a wireless communication system.

The disclosure may provide the device and method for configuring acandidate target cell when performing a conditional handover (CHO) inthe wireless communication system.

The disclosure provides the device and method for managing candidatecell configurations by using a candidate cell ID of a candidate cell forCHO in the wireless communication system.

The disclosure provides the device and method for performing signalingbased on an applicability check for the candidate cell configurations inthe wireless communication system.

According to embodiments, a method performed by a user equipment (UE) ina wireless communication system, the method comprises: receiving, from abase station, a radio resource control (RRC) reconfiguration messageincluding conditional configuration information, and a configuration ofthe candidate cell; and performing one or more operations for aconditional handover based on RRC reconfiguration message. Theconditional configuration information includes: identificationinformation for a candidate cell.

According to embodiments, a method performed by a base station in awireless communication system, comprises generating a radio resourcecontrol (RRC) reconfiguration message including conditionalconfiguration information, wherein the conditional configurationinformation includes: identification information for a candidate cell;and a configuration of the candidate cell; and transmitting, to a userequipment (UE), a radio resource control (RRC) reconfiguration messagefor a conditional handover.

According to embodiments, a user equipment (UE) in a wirelesscommunication system, comprising: at least one transceiver; and at leastone processor configured to: receive, from a base station via the atleast one transceiver, a radio resource control (RRC) reconfigurationmessage including conditional configuration information; and perform oneor more operations for a conditional handover based on RRCreconfiguration message. The conditional configuration informationincludes: identification information for a candidate cell; and aconfiguration of the candidate cell.

According to embodiments, a base station in a wireless communicationsystem, comprises at least one transceiver; and at least one processorconfigured to generate a radio resource control (RRC) reconfigurationmessage including conditional configuration information, wherein theconditional configuration information includes: identificationinformation for a candidate cell; and a configuration of the candidatecell; and transmit, to a user equipment (UE) via the at least onetransceiver, a radio resource control (RRC) reconfiguration message fora conditional handover.

According to embodiments, an operation method of a terminal in awireless communication system may include: receiving candidate cellconfigurations for one or more candidate cells for a conditionalhandover (CHO) from a base station; identifying a candidate cellidentifier (ID) for each candidate cell in the candidate cellconfigurations; and on the basis of the candidate cell ID, updating acandidate cell configuration corresponding to the candidate cell ID to alist of candidate cell configurations, which is stored in the terminal,wherein the candidate cell ID may be generated based on at least one ofan ID of the base station or a cell ID of a candidate cell.

According to embodiments, an operation method of a base station in awireless communication system may include: on the basis of at least oneof an identifier (ID) of the base station or a cell ID of a candidatecell for a conditional handover (CHO), generating a candidate cell ID ofthe candidate cell; and transmitting, to a terminal, a candidate cellconfiguration including at least one of the candidate cell ID, a CHOconfiguration, or a CHO trigger condition, wherein at least one of theCHO configuration or the CHO trigger condition is received from anadjacent base station related to the candidate cell via a handoveracknowledgment message for a handover request.

According to embodiments, a terminal in a wireless communication systemmay include: a transceiver configured to receive candidate cellconfigurations for one or more candidate cells for a conditionalhandover (CHO) from a base station; and at least one processorconfigured to identify a candidate cell identifier (ID) for eachcandidate cell in the candidate cell configurations, and update, basedon the candidate cell ID, a candidate cell configuration correspondingto the candidate cell ID to a list of candidate cell configurations,which is stored in the terminal. The candidate cell ID may be generatedbased on at least one of an ID of the base station or an ID of acandidate cell.

According to embodiments, a base station in a wireless communicationsystem may include: at least one processor configured to, based on atleast one of an identifier (ID) of the base station or a cell ID of acandidate cell for a conditional handover (CHO), generate a candidatecell ID of the candidate cell; and a transceiver configured to transmit,to a terminal, a candidate cell configuration including at least one ofthe candidate cell ID, a CHO configuration, or a CHO trigger condition,wherein at least one of the CHO configuration or the CHO triggercondition is received from an adjacent base station related to thecandidate cell via a handover acknowledgment message for a handoverrequest.

A device and method according to embodiments can reduce signalingoverhead by instructing a change of a candidate cell configuration onthe basis of a candidate cell identifier (ID).

The device and method according to embodiments can increase a handoversuccess rate by notifying a network of a candidate cell ID of acandidate cell for which an applicability check has failed, andperforming a CHO for a candidate cell for which an applicability checkhas been successfully performed.

Various respective aspects and features of the invention are defined inthe appended claims. Combinations of features from the dependent claimsmay be combined with features of the independent claims as appropriateand not merely as explicitly set out in the claims.

Furthermore, one or more selected features of any one embodimentdescribed in this disclosure may be combined with one or more selectedfeatures of any other embodiment described herein, provided that thealternative combination of features at least partially alleviates theone or more technical problem discussed in this disclosure or at leastpartially alleviates a technical problem discernable by the skilledperson from this disclosure and further provided that the particularcombination or permutation of embodiment features thus formed would notbe understood by the skilled person to be incompatible.

Two or more physically distinct components in any described exampleimplementation of this disclosure may alternatively be integrated into asingle component where possible, provided that the same function isperformed by the single component thus formed. Conversely, a singlecomponent of any embodiment described in this disclosure mayalternatively be implemented as two or more distinct components toachieve the same function, where appropriate.

It is an aim of certain embodiments of the invention to solve, mitigateor obviate, at least partly, at least one of the problems and/ordisadvantages associated with the prior art. Certain embodiments aim toprovide at least one of the advantages described below.

Effects obtainable from the disclosure may not be limited to the abovementioned effects, and other effects which are not mentioned may beclearly understood, through the following descriptions, by those skilledin the art to which the disclosure pertains.

Before undertaking the DETAILED DESCRIPTION below, it may beadvantageous to set forth definitions of certain words and phrases usedthroughout this patent document: the terms “include” and “comprise,” aswell as derivatives thereof, mean inclusion without limitation; the term“or,” is inclusive, meaning and/or; the phrases “associated with” and“associated therewith,” as well as derivatives thereof, may mean toinclude, be included within, interconnect with, contain, be containedwithin, connect to or with, couple to or with, be communicable with,cooperate with, interleave, juxtapose, be proximate to, be bound to orwith, have, have a property of, or the like; and the term “controller”means any device, system or part thereof that controls at least oneoperation, such a device may be implemented in hardware, firmware orsoftware, or some combination of at least two of the same. It should benoted that the functionality associated with any particular controllermay be centralized or distributed, whether locally or remotely.

Moreover, various functions described below can be implemented orsupported by one or more computer programs, each of which is formed fromcomputer readable program code and embodied in a computer readablemedium. The terms “application” and “program” refer to one or morecomputer programs, software components, sets of instructions,procedures, functions, objects, classes, instances, related data, or aportion thereof adapted for implementation in a suitable computerreadable program code. The phrase “computer readable program code”includes any type of computer code, including source code, object code,and executable code. The phrase “computer readable medium” includes anytype of medium capable of being accessed by a computer, such as readonly memory (ROM), random access memory (RAM), a hard disk drive, acompact disc (CD), a digital video disc (DVD), or any other type ofmemory. A “non-transitory” computer readable medium excludes wired,wireless, optical, or other communication links that transporttransitory electrical or other signals. A non-transitory computerreadable medium includes media where data can be permanently stored andmedia where data can be stored and later overwritten, such as arewritable optical disc or an erasable memory device.

Definitions for certain words and phrases are provided throughout thispatent document, those of ordinary skill in the art should understandthat in many, if not most instances, such definitions apply to prior, aswell as future uses of such defined words and phrases.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of certainembodiments of the disclosure will be more apparent from the followingdescription taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 illustrates a wireless communication system according to variousembodiments;

FIG. 2 illustrates a configuration of a base station in the wirelesscommunication system according to various embodiments;

FIG. 3 illustrates a configuration of a terminal in the wirelesscommunication system according to various embodiments;

FIG. 4 illustrates a configuration of a communication unit in thewireless communication system according to various embodiments;

FIG. 5 illustrates an example of a structure of the wirelesscommunication system according to various embodiments;

FIG. 6 illustrates an example of a wireless protocol structure in thewireless communication system according to various embodiments;

FIG. 7 illustrates another example of the structure of the wirelesscommunication system according to various embodiments;

FIG. 8 illustrates another example of the wireless protocol structure inthe wireless communication system according to various embodiments;

FIG. 9 illustrates an example of a case in which a serving node receivesCHO configuration information from a target node and then assigns a CHOcandidate cell ID in the wireless communication system according tovarious embodiments;

FIG. 10 illustrates an example of a case in which a serving node assignsa CHO candidate cell ID and then transmits a handover request message toa target node in the wireless communication system according to variousembodiments;

FIG. 11 illustrates an example of a case of modifying a candidate cellconfiguration by using a candidate cell ID in the wireless communicationsystem according to various embodiments;

FIG. 12 illustrates an example of a case of releasing a candidate cellconfiguration on the basis of a candidate cell ID in the wirelesscommunication system according to various embodiments;

FIG. 13 illustrates an example of a case of releasing a candidate cellconfiguration when a CHO is performed in the wireless communicationsystem according to various embodiments;

FIG. 14 illustrates an example of a case of releasing a candidate cellconfiguration after a CHO is successfully performed in the wirelesscommunication system according to various embodiments;

FIG. 15 illustrates an example of a case of performing an applicabilitycheck in the wireless communication system according to variousembodiments;

FIG. 16 illustrates an example of a case of, if an applicability checkfor a CHO candidate cell configuration is successful, transmitting anRRC reconfiguration completion message to a source cell in the wirelesscommunication system according to various embodiments;

FIG. 17 illustrates an example of a case of, if an applicability checkfor a CHO candidate cell configuration is successful, transmitting anRRC reconfiguration completion message to a target cell in the wirelesscommunication system according to various embodiments;

FIG. 18 illustrates an example of a case of, if an applicability checkfor a CHO candidate cell configuration has failed, transmitting afailure message in the wireless communication system according tovarious embodiments;

FIG. 19 illustrates an example of a case of, if an applicability checkfor a CHO candidate cell configuration has failed, performing an RRCconnection re-establishment procedure in the wireless communicationsystem according to various embodiments;

FIG. 20 illustrates an example of a case of, if an applicability checkfor a plurality of CHO candidate cell configurations is successful,transmitting an RRC reconfiguration completion message in the wirelesscommunication system according to various embodiments;

FIG. 21 illustrates an example of a case of, if an applicability checkfor a plurality of CHO candidate cell configurations is successful,performing a CHO and then transmitting an RRC reconfiguration completionmessage in the wireless communication system according to variousembodiments;

FIG. 22 illustrates an example of a case of, if an applicability checkfor some candidate cell configurations among a plurality of CHOcandidate cell configurations has failed, transmitting a failure messagein the wireless communication system according to various embodiments;

FIG. 23 illustrates an example of a case of, if an applicability checkfor some candidate cell configurations among a plurality of CHOcandidate cell configurations has failed, performing RRE in the wirelesscommunication system according to various embodiments;

FIG. 24 illustrates an example of a case of performing an applicabilitycheck for a candidate cell configuration for a candidate cell thatsatisfies a CHO trigger condition in the wireless communication systemaccording to various embodiments;

FIG. 25 illustrates an example of a case of receiving CHO candidate cellconfigurations for a plurality of candidate cells together with areconfiguration related to a current serving cell in the wirelesscommunication system according to various embodiments; and

FIG. 26 illustrates a flowchart of a terminal in a case of receiving CHOcandidate cell configurations for a plurality of candidate cellstogether with a reconfiguration related to a current serving cell in thewireless communication system according to various embodiments.

DETAILED DESCRIPTION

FIGS. 1 through 26, discussed below, and the various embodiments used todescribe the principles of the present disclosure in this patentdocument are by way of illustration only and should not be construed inany way to limit the scope of the disclosure. Those skilled in the artwill understand that the principles of the present disclosure may beimplemented in any suitably arranged system or device.

The terms used in the disclosure are only used to describe specificembodiments, and are not intended to limit the disclosure. A singularexpression may include a plural expression unless they are definitelydifferent in a context. Unless defined otherwise, all terms used herein,including technical and scientific terms, have the same meaning as thosecommonly understood by a person skilled in the art to which thedisclosure pertains. Such terms as those defined in a generally useddictionary may be interpreted to have the meanings equal to thecontextual meanings in the relevant field of art, and are not to beinterpreted to have ideal or excessively formal meanings unless clearlydefined in the disclosure. In some cases, even the term defined in thedisclosure should not be interpreted to exclude embodiments of thedisclosure.

Hereinafter, various embodiments of the disclosure will be describedbased on an approach of hardware. However, various embodiments of thedisclosure include a technology that uses both hardware and software,and thus the various embodiments of the disclosure may not exclude theperspective of software.

Hereinafter, various embodiments provide a device and method forperforming a handover in a wireless communication system. Morespecifically, various embodiments provide the device and method forperforming a conditional handover (CHO) in the wireless communicationsystem. In various embodiments, the CHO may refer to selecting onetarget cell from among candidate cells that satisfy a CHO triggercondition and performing a handover to the selected target cell, by aterminal.

Hereinafter, terms referring to a signal to be used, terms referring toa channel, terms referring to control information, terms referring tonetwork entities, terms referring to elements of a device, and the likeare illustrated for convenience of explanation. Therefore, thedisclosure is not limited to the terms described below, and other termshaving equivalent technical meanings may be used.

The disclosure describes various embodiments by using terms used in somecommunication specifications (e.g., 3rd generation partnership project(3GPP)), but this is merely illustrative. Various embodiments may alsobe easily modified and applied to other communication systems.

In particular, the disclosure may be applied to 3GPP new radio (NR), or5th generation (5G) mobile communication standards. The disclosure maybe applied to intelligent services (for example, smart homes, smartbuildings, smart cities, smart cars or connected cars, health care,digital education, retail business, security and safety-relatedservices, etc.) on the basis of a 5G communication technology and anInternet of things (IoT)-related technology.

A wireless communication system has moved away from providing earlyvoice-oriented services, and advances in broadband wirelesscommunication systems that provide high-speed and high-quality packetdata services, such as communication standards, for example, 3GPP's highspeed packet access (HSPA), long term evolution (LTE) or evolveduniversal terrestrial radio access (E-UTRA), LTE-advanced (LTE-A),LTE-Pro, 3GPP2's high rate packet data (HRPD), ultra-mobile broadband(UMB), IEEE's 802.16e, and the like.

As a representative example of a broadband wireless communicationsystem, an LTE system adopts an orthogonal frequency divisionmultiplexing (OFDM) scheme as a multiple access scheme in a downlink(DL), and adopts a single carrier frequency division multiple access(SC-FDMA) scheme and/or an OFDM scheme as a multiple access scheme in anuplink (UL). Uplink refers to a wireless link via which a terminal (userequipment (e.g., UE) or a mobile station (MS) transmits data or acontrol signal to a base station (BS) (e.g., eNodeB), and downlinkrefers to a wireless link via which a base station transmits data or acontrol signal to a terminal. In such a multiple-access scheme, data orcontrol information of each user may be distinguished by assigning andoperating time-frequency resources, at which data or control informationof each user is transmitted, so as not to overlap each other, that is,to establish orthogonality.

A 5G communication system, as a future communication system after LTE,should be able to freely reflect various requirements of users andservice providers, so that the 5G communication system should be able tosupport services that simultaneously satisfy various requirements. Forexample, services considered for the 5G communication system may includean enhanced mobile broadband (eMBB), massive machine type communication(mMTC), and ultra-reliability low latency communication.

According to an embodiment, the eMBB may aim to provide a datatransmission rate that is further improved than a data transmission ratesupported by existing LTE, LTE-A, or LTE-Pro. For example, in the 5Gcommunication system, an eMBB should be able to provide a maximum datarate of 20 Gbps in a downlink and a maximum data rate of 10 Gbps in anuplink from the perspective of one base station. The 5G communicationsystem may need to provide a maximum transmission rate while providingan increased actual perceived data rate (user perceived data rate) of aterminal. In order to satisfy these requirements, in the 5Gcommunication system, improvement of various transmission/receptiontechnologies including a more advanced multi-input multi-output (MIMO)transmission technology may be required. In addition, in a band of 2 GHzused by current LTE, a signal is transmitted using a maximumtransmission bandwidth of 20 MHz, whereas, in the 5G communicationsystem, a data transmission rate, which is required by the 5Gcommunication system, may be satisfied by using a frequency bandwidthwider than 20 MHz in a frequency band of 3 to 6 GHz or 6 GHz or higher.

At the same time, mMTC is being considered to support applicationservices, such as the Internet of Things (IoT), in the 5G communicationsystem. In order to efficiently provide the Internet of Things, mMTC mayrequire support for large-scale terminal access in a cell, improvedcoverage of the terminal, an improved battery time, and a reduced costof the terminal. In the Internet of Things, since terminals are attachedto various sensors and various devices to provide communicationfunctions, the Internet of Things should be able to support a largenumber of terminals (e.g., 1,000,000 terminals/km2) in a cell. Due tothe nature of a service, a terminal that supports mMTC is likely to belocated in a shaded area that cannot be covered by a cell, such as thebasement of a building, and therefore a wider coverage may be requiredin mMTC compared to other services provided by the 5G communicationsystem. The terminal that supports mMTC may be required to be a low-costterminal, and since it is difficult to frequently exchange a battery ofthe terminal, a very long battery life time, such as 10 to 15 years, maybe required in mMTC.

Finally, URLLC is a cellular-based wireless communication service usedfor mission-critical purposes, and may include a remote control for arobot or machinery, industrial automation, an unmanned aerial vehicle,remote health care, and an emergency alert. Therefore, communicationprovided by URLLC may need to provide a very low latency (ultra-lowlatency) and a very high reliability (super reliability). For example, aservice that supports URLLC should satisfy an air interface latency lessthan 0.5 milliseconds, and at the same time, may have a requirement of apacket error rate of 10-5 or less. Therefore, for the service thatsupports URLLC, the 5G system should provide a transmission timeinterval (TTI) smaller than that of other services, and at the sametime, in order to secure the reliability of a communication link, adesign requirement that a wide resource should be allocated in afrequency band may be required in the 5G system.

Three services considered in the above-mentioned 5G communicationsystem, which are eMBB, URLLC, and mMTC, may be multiplexed and providedin one system. At this time, different transmission/reception techniquesand transmission/reception parameters may be used between services tosatisfy different requirements of respective services. However, theabove-described mMTC, URLLC, and eMBB are merely examples of differentservice types, and service types to which the disclosure is applied arenot limited to the above-described examples.

Hereinafter, embodiments are described as an example of an LTE, LTE-A,LTE Pro, or 5G (or NR or next-generation mobile communication) system,but embodiments may be applied to other communication systems having asimilar technical background or channel type. Further, embodiments maybe applied to other communication systems via some modifications withoutdeparting from the scope of the disclosure, according to determinationby those skilled in the art.

Definitions of terms used in various embodiments are as follows.

A “CHO candidate cell” refers to a candidate cell that may be a targetcell of CHO. In various embodiments, the “CHO candidate cell” may bereferred to as a “candidate cell” or a “candidate target cell”.

A “candidate cell configuration” or a “CHO candidate cell configuration”may be defined for each candidate cell and may include one or moreCHO-related configurations for each candidate cell. For example, thecandidate cell configuration may include at least one of a CHO candidatecell ID for each candidate cell, a CHO configuration for each candidatecell, or a CHO trigger condition for each candidate cell.

A “CHO candidate cell ID” refers to an ID of a CHO candidate cell.

A “CHO configuration” or “CHO configuration information” refers toconfiguration information related to CHO. In various embodiments, theCHO configuration may include a resource configuration for CHO.

A “CHO trigger condition for a candidate cell” refers to a condition totrigger a CHO to a corresponding candidate cell.

A term “SpCell” refers to a primary cell (PCell) or a primary secondarycell (PSCell). For Dual Connectivity operation the term Special Cellrefers to the PCell of the master cell group (MCG) or the PSCell of thesecondary cell group (SCG) depending on if the MAC entity is associatedto the MCG or the SCG, respectively. Otherwise the term Special Cellrefers to the PCell.

An operation “update” refers to a replacement of a previous one with anew one.

An “applicability check for configuration/reconfiguration” refers tocheck whether a UE can apply a configuration or reconfiguration receivedfrom a base station. A failure of the applicability check refers to acase in which all or a part of received configuration or reconfigurationinformation includes a configuration value that the UE cannot apply. Onthe other hand, a success of the applicability check refers to a case inwhich the UE can apply received configuration or reconfigurationinformation. In various embodiments, an applicability check may also bereferred to as a “compliance check”.

FIG. 1 illustrates a wireless communication system according to variousembodiments. FIG. 1 illustrates a base station 110, a terminal 120, anda terminal 130, as parts of nodes using a wireless channel in a wirelesscommunication system. FIG. 1 illustrates only one base station, but mayfurther include another base station that is the same as or similar tothe base station 110.

The base station 110 is a network infrastructure that provides wirelessaccess to the terminals 120 and 130. The base station 110 has coveragedefined as a predetermined geographic area on the basis of the distanceover which a signal may be transmitted. The base station 110 may bereferred to as, in addition to “base station”, “access point (AP)”,“eNodeB (eNB)”, “5G node (5th generation node)”, “next generation nodeB(gNB)”, “wireless point”, “transmission/reception point (TRP)”, or otherterms having equivalent technical meanings.

Each of the terminal 120 and the terminal 130 is a device used by auser, and performs communication with the base station 110 via thewireless channel. In some cases, at least one of the terminal 120 andthe terminal 130 may be operated without involvement of a user. That is,at least one of the terminal 120 and the terminal 130 is a device thatperforms machine type communication (MTC) and may not be carried by auser. Each of the terminal 120 and the terminal 130 may be referred toas, in addition to “terminal”, “user equipment (UE)”, “mobile station”,“subscriber station”, “remote terminal”, “wireless terminal”, “userdevice”, or other terms having equivalent technical meanings.

The base station 110, the terminal 120, and the terminal 130 maytransmit and receive wireless signals in a millimeter wave band (e.g.,28 GHz, 30 GHz, 38 GHz, and 60 GHz).

At this time, in order to improve a channel gain, the base station 110,the terminal 120, and the terminal 130 may perform beamforming. Thebeamforming may include transmission beamforming and receptionbeamforming. That is, the base station 110, the terminal 120, and theterminal 130 may assign a directivity to a transmission signal or areception signal. To this end, the base station 110 and the terminals120 and 130 may select serving beams 112, 113, 121, and 131 via a beamsearch procedure or a beam management procedure. After the serving beams112, 113, 121, and 131 are selected, communication may then be performedvia resources that are in quasi co-located (QCL) relationship withresources at which the serving beams 112, 113, 121, and 131 aretransmitted.

If it is possible to infer large-scale characteristics of a channel fortransferring of a symbol on a first antenna port, from a channel fortransferring of a symbol on a second antenna port, then it may beestimated that the first antenna port and the second antenna port are ina QCL relationship. For example, the large-scale characteristics mayinclude at least one among a delay spread, a Doppler spread, a Dopplershift, an average gain, an average delay, and a spatial receiverparameter.

FIG. 2 illustrates a configuration of a base station in the wirelesscommunication system according to various embodiments. The configurationillustrated in FIG. 2 may be understood as a configuration of the basestation 110. The terms “˜ unit”, “˜ device”, etc. used hereinafter referto a unit that processes at least one function or operation, which maybe implemented by hardware or software, or a combination of hardware andsoftware.

Referring to FIG. 2, the base station includes a wireless communicationunit 210, a backhaul communication unit 220, a storage unit 230, and acontroller 240.

The wireless communication unit 210 performs functions to transmit orreceive a signal through a wireless channel. For example, the wirelesscommunication unit 210 performs conversion between a baseband signal anda bitstream according to a physical layer specification of a system. Forexample, during data transmission, the wireless communication unit 210generates complex symbols by encoding and modulating a transmissionbitstream. When receiving data, the wireless communication unit 210restores the received bitstream by demodulating and decoding thebaseband signal.

Further, the wireless communication unit 210 up-converts the basebandsignal to a radio frequency (RF) band signal, transmits the up-convertedRF band signal via an antenna, and then down-converts the RF band signalreceived via the antenna to a baseband signal. To this end, the wirelesscommunication unit 210 may include a transmission filter, a receptionfilter, an amplifier, a mixer, an oscillator, a digital-to-analogconverter (DAC), an analog-to-digital converter (ADC), and the like.Also, the wireless communication unit 210 may include multipletransmission/reception paths. Further, the wireless communication unit210 may include at least one antenna array including multiple antennaelements.

In terms of hardware, the wireless communication unit 210 may include adigital unit and an analog unit, wherein the analog unit includesmultiple sub-units according to an operating power, an operatingfrequency, and the like. The digital unit may be implemented as at leastone processor (e.g., a digital signal processor (DSP)).

The wireless communication unit 210 transmits and receives a signal asdescribed above. Accordingly, all or a part of the wirelesscommunication unit 210 may be referred to as a “transmitter”, a“receiver”, or a “transceiver”. In the following description,transmission and reception performed via a wireless channel are used ina sense including processing performed as described above by thewireless communication unit 210.

The backhaul communication unit 220 provides an interface that performscommunication with other nodes within a network. That is, the backhaulcommunication unit 220 converts, into a physical signal, a bitstreamtransmitted from a base station to another node, for example, anotheraccess node, another base station, an upper node, a core network, etc.,and converts a physical signal received from another node into abitstream.

The storage unit 230 stores data, such as a basic program, anapplication program, configuration information, and the like foroperation of the base station. The storage unit 230 may include avolatile memory, a nonvolatile memory, or a combination of a volatilememory and a nonvolatile memory. The storage unit 230 provides storeddata in response to a request of the controller 240.

The controller 240 controls overall operations of the base station. Forexample, the controller 240 transmits and receives a signal via thewireless communication unit 210 or the backhaul communication unit 220.Further, the controller 240 records and reads data in the storage unit230. The controller 240 may perform functions of a protocol stackrequired by the communication standard. According to another implement,the protocol stack may be included in the wireless communication unit210. To this end, the controller 240 may include at least one processor.

According to various embodiments, the controller 240 may control thebase station to perform operations according to various embodimentsdescribed below.

FIG. 3 illustrates a configuration of a terminal in the wirelesscommunication system according to various embodiments. The configurationillustrated in FIG. 3 may be understood as a configuration of theterminal 120. The terms “˜ unit”, “˜ device”, etc. used hereinafterrefer to a unit that processes at least one function or operation, whichmay be implemented by hardware or software, or a combination of hardwareand software.

Referring to FIG. 3, the terminal may include a communication unit 310,a storage unit 320, and a controller 330.

The communication unit 310 performs functions for transmitting orreceiving a signal via a wireless channel. For example, thecommunication unit 310 performs conversion between a baseband signal anda bitstream according to a physical layer specification of the system.For example, during data transmission, the communication unit 310generates complex symbols by encoding and modulating a transmissionbitstream. When receiving data, the communication unit 310 restores thereceived bitstream by demodulating and decoding the baseband signal. Thecommunication unit 310 up-converts the baseband signal into an RF bandsignal, transmits the up-converted RF band signal via an antenna, andthen down-converts the RF band signal received via the antenna into abaseband signal. For example, the communication unit 310 may include atransmission filter, a reception filter, an amplifier, a mixer, anoscillator, a DAC, an ADC, and the like.

Also, the communication unit 310 may include a plurality oftransmission/reception paths. Further, the communication unit 310 mayinclude at least one antenna array including multiple antenna elements.In terms of hardware, the communication unit 310 may include a digitalcircuit and an analog circuit (e.g., a radio frequency integratedcircuit (RFIC)). The digital circuit and the analog circuit may beimplemented in a single package. The communication unit 310 may includea plurality of RF chains. Further, the communication unit 310 mayperform beamforming.

The communication unit 310 transmits and receives a signal as describedabove. Accordingly, all or a part of the communication unit 310 may bereferred to as “transmitter”, “receiver”, or “transceiver”. In thefollowing description, transmission and reception performed via awireless channel are used in a sense including processing performed asdescribed above by the wireless communication unit 310.

The storage unit 320 stores data, such as a basic program, anapplication program, configuration information, and the like foroperation of the terminal. The storage unit 320 may include a volatilememory, a nonvolatile memory, or a combination of a volatile memory anda nonvolatile memory. The storage unit 320 provides stored data inresponse to a request of the controller 330.

The controller 330 controls overall operations of the terminal. Forexample, the controller 330 transmits and receives a signal via thecommunication unit 310. Further, the controller 330 records and readsdata in the storage unit 320. The controller 330 may perform functionsof a protocol stack required by the communication standard. To this end,the controller 330 may include at least one processor or amicro-processor, or may be a part of a processor. A part of thecommunication unit 310 and the controller 330 may be referred to as acommunication processor (CP).

According to various embodiments, the controller 330 may control theterminal to perform operations according to various embodimentsdescribed below.

FIG. 4 illustrates a configuration of a communication unit in thewireless communication system according to various embodiments. FIG. 4illustrates an example of a detailed configuration of the wirelesscommunication unit 210 of FIG. 2 or the communication unit 310 of FIG.3. Specifically, FIG. 4 illustrates elements to perform beamforming, asa part of the wireless communication unit 210 of FIG. 2 or thecommunication unit 310 of FIG. 3.

Referring to FIG. 4, the wireless communication unit 210 or thecommunication unit 310 includes an encoder and modulator 402, a digitalbeamformer 404, a plurality of transmission paths 406-1 to 406-N, and ananalog beamformer 408.

The encoder and modulator 402 performs channel encoding. For channelencoding, at least one among a low density parity check (LDPC) code, aconvolution code, a polar code may be used. The encoder and modulator402 generates modulation symbols by performing constellation mapping.

The digital beamformer 404 performs beamforming on a digital signal(e.g., modulation symbols). To this end, the digital beamformer 404multiplies modulation symbols by beamforming weights. Here, thebeamforming weights are used to change a magnitude and phase of asignal, and may be referred to as “a precoding matrix”, “a precoder”, orthe like. The digital beamformer 404 outputs digital-beamformedmodulation symbols to the plurality of transmission paths 406-1 to406-N. According to a multiple input multiple output (MIMO) transmissiontechnique, the modulation symbols may be multiplexed or the samemodulation symbols may be provided to the plurality of transmissionpaths 406-1 to 406-N.

The plurality of transmission paths 406-1 to 406-N convert digitalbeamformed-signals into analog-signals. To this end, each of theplurality of transmission paths 406-1 to 406-N may include an inversefast Fourier transform (IFFT) calculation unit, a cyclic prefix (CP)insertion unit, a DAC, and an up-conversion unit. The CP insertion unitis for an orthogonal frequency division multiplexing (OFDM) scheme, andmay be excluded when another physical layer scheme (e.g., a filter bankmulti-carrier (FBMC)) is applied. That is, the plurality of transmissionpaths 406-1 to 406-N provide independent signal processing processes toa plurality of streams generated via digital beamforming. However,depending on an implementation scheme, some elements of the plurality oftransmission paths 406-1 to 406-N may be used in common.

The analog beamformer 408 performs beamforming on an analog signal. Tothis end, the digital beamformer 404 multiplies analog signals bybeamforming weights. The beamforming weights are used to change amagnitude and a phase of a signal. Specifically, according to aconnection structure between the plurality of transmission paths 406-1to 406-N and antennas, the analog beamformer 440 may be configured invarious manners. For example, each of the plurality of transmissionpaths 406-1 to 406-N may be connected to one antenna array. As anotherexample, the plurality of transmission paths 406-1 to 406-N may beconnected to one antenna array. As still another example, the pluralityof transmission paths 406-1 to 406-N may be adaptively connected to oneantenna array or may be connected to two or more antenna arrays.

FIG. 5 illustrates an example of a structure of the wirelesscommunication system according to various embodiments. The wirelesscommunication system illustrated in FIG. 5 may be an LTE system.

Referring to FIG. 5, a radio access network of the LTE system mayinclude eNBs 521, 523, 525, and 527, a mobility management entity (MME)530, and a serving gateway (S-GW) 540. A UE 510 may access at least oneof the eNBs 521, 523, 525, and 527 and an external network via the S-GW540.

In FIG. 5, the eNBs 521, 523, 525, and 527 may correspond to node B of auniversal mobile telecommunication system (UMTS). The eNB 521 isconnected to the UE 510 via a wireless channel, and may perform a morecomplex role than node B. In the LTE system, all user traffic includinga real-time service, such as a voice over Internet protocol (VoIP) viathe Internet protocol, may be serviced through a shared channel.Accordingly, a device that performs scheduling based on stateinformation, such as buffer states, available transmission power states,and channel states of UEs, may be needed, and such a device may be theeNBs 521, 523, 525, and 527. One eNB (e.g., the eNB 521) may controlmultiple cells. For example, in order to realize a transmission rate of100 Mbps, the LTE system may use OFDM as a radio access technology, forexample, in a bandwidth of 20 megaHertz (MHz). Further, the eNB (e.g.,eNB 521) may use an adaptive modulation & coding (AMC) scheme fordetermining a channel coding rate and a modulation scheme on the basisof the channel state of a terminal. The S-GW 540 is a device thatprovides a data bearer, and may generate or eliminate a data bearerunder the control of the MME 530. The MME 530 is a device that is incharge of mobility management functions and various control functionsfor the terminal (e.g., the UE 510), and may be connected to a pluralityof base stations (e.g., the eNBs 521, 523, 525, and 527).

FIG. 6 illustrates an example of a wireless protocol structure in thewireless communication system according to various embodiments. Thewireless communication system illustrated in FIG. 6 may be an LTEsystem.

Referring to FIG. 6, a wireless protocols of the LTE system may include,in the terminal 120 and the eNB 110, packet data convergence protocols(PDCPs) 611 and 621, radio link controls (RLCs) 713 and 723, mediumaccess controls (MACs) 715 and 725, and physical layers (PHYs) 617 and627, respectively. The PDCPs 611 and 621 may perform operations, such asIP header compression/restoration. Main functions of PDCPs 611 and 621include at least one of the following examples, but are not limited tothe following examples:

-   -   a header compression and decompression function (ROHC)    -   a user data transmission function (transfer of user data)    -   a sequential delivery function (in-sequence delivery of upper        layer PDUs at PDCP re-establishment procedure for RLC AM)    -   a reordering function (for split bearers in dual connectivity        (only support for RLC AM): PDCP PDU routing for transmission and        PDCP PDU reordering for reception)    -   a duplicate detection function (duplicate detection of lower        layer SDUs at PDCP re-establishment procedure for RLC AM)    -   a retransmission function (retransmission of PDCP SDUs at        handover and, for split bearers in DC, of PDCP PDUs at PDCP        data-recovery procedure, for RLC AM)    -   an encryption and decryption function (ciphering and        deciphering)    -   a timer-based SDU delete function (timer-based SDU discard in        uplink)

According to an embodiment, the RLCs 613 and 623 may reconfigure a PDCPpacket data unit (PDU) to an appropriate size so as to performoperations, such as an automatic repeat request (ARQ). Main functions ofthe RLCs 613 and 623 include at least one of the following examples, butare not limited to the following examples:

-   -   a data transmission function (transfer of upper layer PDUs)    -   an ARQ function (error correction through ARQ (only for AM data        transfer))    -   a concatenation, segmentation, and reassembly function        (concatenation, segmentation, and reassembly of RLC SDUs (only        for UM and AM data transfer))    -   a re-segmentation function (re-segmentation of RLC data PDUs        (only for AM data transfer))    -   a reordering function (reordering of RLC data PDUs (only for UM        and AM data transfer)    -   a duplicate detection function (duplicate detection (only for UM        and AM data transfer))    -   an error detection function (protocol error detection (only for        AM data transfer))    -   an RLC SDU deletion function (RLC SDU discard (only for UM and        AM data transfer))    -   an RLC re-establishment function (RLC re-establishment)

According to an embodiment, the MACs 615 and 625 may be connected tovarious RLC layer devices configured in the UE (terminal) 120, and mayperform an operation of multiplexing RLC PDUs to a MAC PDU anddemultiplexing RLC PDUs from the MAC PDU. Main functions of the MACs 715and 717 include at least one of the following examples, but are notlimited to the following examples:

-   -   a mapping function (mapping between logical channels and        transport channels)    -   a multiplexing and demultiplexing function        (multiplexing/demultiplexing of MAC SDUs belonging to one or        different logical channels into/from transport blocks (TB)        delivered to/from the physical layer on transport channels)    -   a scheduling information reporting function (scheduling        information reporting)    -   a HARQ function (error correction through HARQ)    -   a function of adjusting priority between logical channels        (priority handling between logical channels of one UE)    -   a function of adjusting priority between UEs (priority handling        between UEs by means of dynamic scheduling)    -   an MBMS service identification function (MBMS service        identification)    -   a transmission format selection function (transport format        selection)    -   a padding function (padding)

According to an embodiment, PHY 617 and 627 may perform channel-codingand modulation of upper layer data, converting the channel-coded andmodulated upper layer data into OFDM symbols and transmitting theconverted OFDM symbols via a wireless channel, or demodulating andchannel-decoding the OFDM received through the wireless channel andtransferring the same to the upper layer.

FIG. 7 illustrates another example of the structure of the wirelesscommunication system according to various embodiments. The wirelesscommunication system illustrated in FIG. 7 may be an NR system.

Referring to FIG. 7, a wireless access network of the NR system mayinclude an NR gNB 721 and an NR core network (CN) 730. An NR UE 710(e.g., the terminal 120) may access an external network via the NR gNB721 and the NR CN 730.

In FIG. 7, the NR gNB 721 may correspond to an eNB of the LTE system.The NR gNB 721 is connected to the NR UE 710 via a wireless channel andmay provide a more superior service than a node B and/or an eNB. In theNR system, all user traffic may be serviced via a shard channel.Accordingly, a device that performs scheduling based on stateinformation, such as buffer states, available transmission power states,and channel states of UEs, may be needed, and such a device may be theNR gNB 721. The NR gNB 721 may control multiple cells. In the NR system,in order to implement ultra-fast data transmission compared to LTE, abandwidth greater than or equal to a maximum bandwidth supported by LTEmay be applied. In the NR system, OFDM may be used as a wireless accesstechnology, and a beamforming technology may be additionally used.

According to an embodiment, the NR gNB 721 may use an AMC scheme thatdetermines a modulation scheme and a channel coding rate on the basis ofa channel state for the UE 710. The NR CN 730 may perform functions,such as mobility support, a bearer configuration, and a quality ofservice (QoS) configuration. The NR CN 730 may perform mobilitymanagement functions and various control functions for the UE 710, andmay be connected to multiple base stations.

According to various embodiments, the NR system may interwork with theLTE system. In this case, the NR CN 730 may be connected to an MME 740via a network interface. The MME 740 may be connected to an eNB 723 thatis a base station of the LTE system.

FIG. 8 illustrates another example of the wireless protocol structure inthe wireless communication system according to various embodiments. Thewireless communication system illustrated in FIG. 8 may be an NR system.

Referring to FIG. 8, a wireless protocol of the NR system may include NRservice data adaptation protocols (SDAPs) 811 and 821, NR PDCPs 813 and823, NR RLCs 815 and 825, NR MACs 817 and 827, and NR PHYs 819 and 829in a UE (e.g., the terminal 120) and an NR base station (e.g., the basestation 110), respectively.

According to an embodiment, main functions of the NR SDAPs 811 and 821include at least one of the following examples, but are not limitedthereto:

-   -   a user data transfer function (transfer of user plane data)    -   a function of mapping a QoS flow and a data bearer for uplink        and downlink (mapping between a QoS flow and a DRB for both DL        and UL)    -   a function of marking a QoS flow ID in uplink and downlink        (marking QoS flow ID in both DL and UL packets)    -   a function of mapping QoS flows to a data bearer for respective        uplink SDAP PDUs (reflective QoS flow to DRB mapping for the UL        SDAP PDUs)

For an SDAP layer device, the terminal 120 may be configured whether touse a header of the SDAP layer device or use a function of the SDAPlayer device for each PDCP layer device, for each bearer, or for eachlogical channel, via a radio resource control (RRC) message. When theSDAP header is configured, the SDAP layer device may indicate theterminal 120 to update or reconfigure mapping information for a QoS flowand a data bearer in uplink and downlink, via an access stratum (AS)quality of service (QoS) reflection configuration 1-bit indicator (ASreflective QoS) and a non-access stratum (NAS) QoS reflectionconfiguration 1-bit indicator (NAS reflective QoS) of the SDAP header.According to an embodiment, the SDAP header may include QoS flow IDinformation indicating a QoS. According to an embodiment, QoSinformation may function as or similar to scheduling information anddata processing priority for supporting a smooth service.

According to an embodiment, main functions of the NR PDCPs 813 and 823include at least one of the following examples, but are not limitedthereto:

-   -   a header compression and decompression function (header        compression and decompression, ROHC only)    -   a user data transmission function (transfer of user data)    -   a sequential delivery function (in-sequence delivery of upper        layer PDUs)    -   a non-sequential delivery function (out-of-sequence delivery of        upper layer PDUs)    -   a reordering function (PDCP PDU reordering for reception)    -   a duplicate detection function (duplicate detection of lower        layer SDUs)    -   a retransmission function (retransmission of PDCP SDUs)    -   an encryption and decryption function (ciphering and        deciphering)    -   a timer-based SDU delete function (timer-based SDU discard in        uplink)

In the above-described functions of the NR PDCPs 813 and 823, thereordering function may refer to a function of reordering PDCP PDUsreceived from a lower layer, in order based on a PDCP sequence number(SN). The reordering function of an NR PDCP device may include afunction of transferring data to an upper layer in the reordered order,may include a function of directly transferring data without consideringthe order, may include a function of reordering and recording lost PDCPPDUs, may include a function of reporting states of the lost PDCP PDUsto a transmission side, or may include a function of requestingretransmission of the lost PDCP PDUs.

According to an embodiment, main functions of the NR RLCs 815 and 825include at least one of the following examples, but are not limitedthereto:

-   -   a data transmission function (transfer of upper layer PDUs)    -   a sequential delivery function (in-sequence delivery of upper        layer PDUs)    -   a non-sequential delivery function (out-of-sequence delivery of        upper layer PDUs)    -   an ARQ function (error Correction through ARQ)    -   a concatenation, segmentation, and reassembly function        (concatenation, segmentation, and reassembly of RLC SDUs)    -   a re-segmentation function (re-segmentation of RLC data PDUs)    -   a reordering function (reordering of RLC data PDUs)    -   a duplicate detection function (duplicate detection)    -   an error detection function (protocol error detection)    -   an RLC SDU deletion function (RLC SDU discard)    -   an RLC re-establishment function (RLC re-establishment)

In the above-described functions of the NR RLCs 815 and 825, thein-sequence delivery may refer to a function of sequentiallytransferring RLC SDUs received from a lower layer to an upper layer.When one RLC SDU is divided into multiple RLC SDUs and received, thein-sequence delivery function of the NR RLC device may include afunction of reassembling the multiple divided RLC SDUs and thentransferring the reassembled RLC SDUs to the upper layer.

The in-sequence delivery function of the NR RLC device may include afunction of rearranging the received RLC PDUs according to an RLCsequence number (SN) or a PDCP sequence number (SN), may include afunction of reordering and recording lost RLC PDUs, may include afunction of reporting states of the lost RLC PDUs to a transmissionside, and may include a function of requesting retransmission for lostRLC PDUs.

The in-sequence delivery function of the NR RLC device may include afunction of, when a lost RLC SDU exists, sequentially transferring, tothe upper layer, only RLC SDUs before the lost RLC SDU.

The in-sequence delivery function of the NR RLC device may include afunction of, if a predetermined timer expires, sequentially transferringall RLC SDUs, which are received before the timer starts, to the upperlayer even if a lost RLC SDU exists.

The in-sequence delivery function of the NR RLC device may include afunction of, if the predetermined timer expires, sequentiallytransferring all RLC SDUs, which have been received so far, to the upperlayer even if a lost RLC SDU exists.

The NR RLC device may process RLC PDUs in the order of receiving the RLCPDUs regardless of the order of sequence numbers (out-of-sequencedelivery) and may transfer the RLC PDUs to the NR PDCP device.

When the NR RLC device receives a segment, segments that are stored in abuffer or to be received at a later time are received, reconstructedinto one complete RLC PDU, and then transmitted to the NR PDCP device.

The NR RLCs 815 and 825 may not perform a concatenation function, inwhich case the NR MACs 817 and 827 perform a concatenation function, ora concatenation function may be replaced by a multiplexing function ofNR MACs 815 and 825.

In the above-described functions of the NR RLCs 815 and 825, theout-of-sequence delivery function of the NR RLC device may refer to afunction of transferring RLC SDUs received from a lower layer to animmediate upper layer regardless of the order. The out-of-sequencedelivery function of the NR RLC device may include a function of, whenone RLC SDU is divided into multiple RLC SDUs and received, reassemblingand transferring the multiple divided RLC SDUs. The out-of-sequencedelivery function of the NR RLC device may include a function of storingthe RLC SNs or PDCP SNs of the received RLC PDUs, arranging the order,and recording lost RLC PDUs.

According to an embodiment, the NR MACs 817 and 827 may be connected tomultiple NR RLC layer devices configured in the terminal 120. Mainfunctions of the NR MACs 817 and 827 include at least one of thefollowing examples, but are not limited to the following examples:

-   -   a mapping function (mapping between logical channels and        transport channels)    -   a multiplexing and demultiplexing function        (multiplexing/demultiplexing of MAC SDUs)    -   a scheduling information reporting function (scheduling        information reporting)    -   a HARQ function (error correction through HARQ)    -   a function of adjusting priority between logical channels        (priority handling between logical channels of one UE)    -   a function of adjusting priority between UEs (priority handling        between UEs by means of dynamic scheduling)    -   an MBMS service identification function (MBMS service        identification)    -   a transmission format selection function (transport format        selection)    -   a padding function (padding)

The NR PHYs 819 and 829 may perform channel-coding and modulation ofupper layer data, converting the channel-coded and modulated upper layerdata into OFDM symbols and transmitting the converted OFDM symbols via awireless channel, or may perform demodulation and channel-decoding ofthe OFDM received through the wireless channel and transferring the sameto the upper layer.

A Conditional Handover (CHO) is defined as a handover that is executedby the UE when one or more handover execution conditions are met. The UEstarts evaluating the execution condition(s) upon receiving the CHOconfiguration, and stops evaluating the execution condition(s) once theexecution condition(s) is met.

The network configures the UE with one or more candidate target SpCellsin the conditional configuration. The UE evaluates the condition of eachconfigured candidate target SpCell. The UE applies the conditionalconfiguration associated with one of the target SpCells which fulfilsassociated execution condition. The network provides the configurationparameters for the target SpCell in the ConditionalReconfigurationinformation.

FIG. 9 illustrates an example of a case in which a serving node receivesCHO configuration information from a target node and then assigns a CHOcandidate cell ID in the wireless communication system according tovarious embodiments. In FIG. 9, a UE 910 may be the terminal 120, and aserving node 920 may be the base station 110. Each of target node 1 930and target node 2 940 may have the elements of the base station 110illustrated in FIG. 2.

Referring to FIG. 9, in operation 901, the UE 910 may receive ameasurement configuration from the serving node 920. For example, the UE910 may be connected to a serving cell and may receive a measurementconfiguration from the serving node 920 related to the serving cell.

In operation 903, the UE 910 may transmit a measurement report to theserving node 920. The UE 910 may perform measurement based on themeasurement configuration and may transmit the measurement reportincluding a measurement result to the serving node 920.

In operation 905, the serving node 920 may transmit a HANDOVER REQUESTmessage to target node 1 930. For example, the serving node 920 maytransmit the HANDOVER REQUEST message for requesting a CHO to targetnode 1 930 related to at least one cell, on the basis of the measurementresult. In various embodiments, the HANDOVER REQUEST message may includehandover (HO) preparation information.

In operation 907, target node 1 930 may transmit a handover requestacknowledgment (ACK) message to the serving node 920. Target node 1 930may reserve a resource to be used by the UE 910 and may transmit theHANDOVER REQUEST ACK message including CHO configuration information forcell 1 of target node 1 930 to the serving node 920.

In operation 909, the serving node 920 may assign a CHO candidate cellID on the basis of a node ID and a cell ID for cell 1 of target node 1930. For example, the serving node 920 may assign the CHO candidate cellID by using information related to an ID of target node 1 930 and/orinformation related to an ID of a target cell (e.g., cell 1) in the CHOconfiguration information. The CHO candidate cell ID assigned inoperation 909 may be the ID of cell 1 of the target node 930.

In operation 911, the serving node 920 may transmit an RRCreconfiguration message to the UE 910. The RRC reconfiguration messagein operation 911 may include a list of one or more candidate cellconfigurations {a CHO candidate cell ID assigned by the serving node920, a CHO configuration for a candidate cell of the CHO candidate cellID, and a CHO trigger condition for the candidate cell}, and the listmay be referred to as “AddModlist”. In various embodiments, for the listof candidate cell configurations, the UE 910 may, based on a candidatecell ID, i) correct a candidate cell configuration for a candidate cellID which the UE 910 already has, and ii) enable a candidate cellconfiguration for a candidate cell ID, which the UE 910 does not have,to be stored in the UE 910.

In operation 913, the UE 910 may determine whether a candidate cell IDstored in the UE 910 exists in the received list. If the candidate cellID stored in the UE 910 exists in the received list, the UE 910 mayupdate a CHO configuration and a CHO trigger condition for the candidatecell ID stored in the UE 910, with a CHO configuration and a CHO triggercondition for the candidate cell ID in the list of received candidatecell configurations. In other words, if the candidate cell ID stored inthe UE 910 exists in the received list, the UE 910 may update thecandidate cell configuration related to the candidate cell ID stored inthe UE 910, with a received candidate cell configuration related to thecorresponding candidate cell ID. In various embodiments, the listreceived from the serving node 920 may include: i) all candidate cellconfigurations for all candidate cells regardless of a candidate cellconfiguration to be changed; ii) candidate cell configurations to bechanged based on the configuration of the UE 910 currently used in theserving cell; or iii) candidate cell configurations changed based onpreviously transmitted candidate cell configurations. When the UE 910updates the candidate cell configuration, if the candidate cell IDstored in the UE 910 exists in the received list, the followingoperations of A), B) or C) may be performed for the cases of i), ii),and iii), respectively. A) The UE 910 may delete the candidate cellconfiguration for the corresponding candidate cell ID stored in the UE910 and may store the received candidate cell configuration related tothe corresponding candidate cell ID. B) With respect to the candidatecell configuration for the corresponding candidate cell ID stored in theUE 910, the UE 910 may change, to the received configurationinformation, configuration information different from the candidate cellconfiguration related to the currently stored corresponding candidatecell ID in comparison with the configuration updated to the receivedcandidate cell configuration on the basis of the configuration of the UEbeing used in the current serving cell, or the UE 910 may newly add andstore the received configuration information. C) The UE 910 may change,to the received configuration information, configuration informationdifferent from the currently received candidate cell configuration amongpreviously received candidate cell configurations, or may newly add andstore the received configuration information. If a candidate cellconfiguration having a candidate cell ID differing from the candidatecell ID stored in the UE 910 exists in the list of the candidate cellconfigurations received from the serving node 920, the UE 910 may storea candidate cell configuration for a new candidate cell ID (e.g., a CHOconfiguration and a CHO trigger condition), may perform measurement on anew candidate cell on the basis of the candidate cell configuration, andmay evaluate whether a CHO trigger condition for the new candidate cellis satisfied.

In operation 915, the serving node 920 may transmit a HANDOVER REQUESTmessage to target node 2 940. For example, the serving node 920 maytransmit the HANDOVER REQUEST message for requesting a CHO to targetnode 2 940 related to at least one cell, on the basis of the measurementresult. In various embodiments, the HANDOVER REQUEST message may includehandover preparation information.

In operation 917, target node 2 940 may transmit a handover requestacknowledgment message to the serving node 920. Target node 2 940 mayreserve a resource to be used by the UE 910 and may transmit theHANDOVER REQUEST ACK message including CHO configuration information forcell 2 of target node 2 940 to the serving node 920.

In operation 919, the serving node 920 may assign a CHO candidate cellID on the basis of a node ID and a cell ID for cell 1 of target node 1940. For example, the serving node 920 may assign a CHO candidate cellID by using information related to an ID of target node 2 940 and/orinformation related to an ID of a target cell (e.g., cell 2) in the CHOconfiguration information. The CHO candidate cell ID assigned inoperation 909 may be an ID for cell 2 of the target node 940.

In operation 921, the serving node 920 may transmit an RRCreconfiguration message to the UE 910. The RRC reconfiguration messagein operation 921 may include a list of one or more candidate cellconfigurations {a CHO candidate cell ID assigned by the serving node920, a CHO configuration for a candidate cell of the CHO candidate cellID, and a CHO trigger condition for the candidate cell}, and the listmay be referred to as “AddModlist”.

In operation 923, the UE 910 may determine whether a candidate cell IDstored in the UE 910 exists in the received list. If the candidate cellID stored in the UE 910 exists in the received list, the UE 910 mayupdate a CHO configuration and a CHO trigger condition for the candidatecell ID stored in the UE 910, with a CHO configuration and a CHO triggercondition for the corresponding candidate cell ID in the list ofreceived candidate cell configurations. In other words, if the candidatecell ID stored in the UE 910 exists in the received list, the UE 910 mayupdate the candidate cell configuration related to the candidate cell IDstored in the UE 910, with the received candidate cell configurationrelated to the corresponding candidate cell ID. In various embodiments,for the list received from the serving node 920 may include: i) allcandidate cell configurations for all candidate cells regardless ofcandidate cell configurations to be changed; ii) candidate cellconfigurations to be changed based on the configuration of the UE 910currently used in the serving cell; or iii) candidate cellconfigurations changed based on previously transmitted candidate cellconfigurations. When the UE 910 updates the candidate cellconfiguration, if the candidate cell ID stored in the UE 910 exists inthe received list, the following operations of A), B) or C) may beperformed for the cases of i), ii), and iii), respectively. A) The UE910 may delete the candidate cell configuration for the correspondingcandidate cell ID stored in the UE 910 and may store the receivedcandidate cell configuration related to the corresponding candidate cellID. B) With respect to the candidate cell configuration for thecorresponding candidate cell ID stored in the UE 910, the UE 910 maychange, to the received configuration information, configurationinformation different from the candidate cell configuration related tothe currently stored corresponding candidate cell ID in comparison withthe configuration updated to the received candidate cell configurationon the basis of the configuration of the UE being used in the currentserving cell, or the UE 910 may newly add and store the receivedconfiguration information. C) The UE 910 may change, to the receivedconfiguration information, configuration information different from thecurrently received candidate cell configuration among previouslyreceived candidate cell configurations, or may newly add and store thereceived configuration information. If a candidate cell configurationhaving a candidate cell ID differing from the candidate cell ID storedin the UE 910 exists in the list of the candidate cell configurationsreceived from the serving node 920, the UE 910 may store a candidatecell configuration for a new candidate cell ID (e.g., a CHOconfiguration and a CHO trigger condition), may perform measurement on anew candidate cell on the basis of the candidate cell configuration, andmay evaluate whether a CHO trigger condition for the new candidate cellis satisfied.

In various embodiments, a CHO candidate cell ID may be generated byconcatenating frequency information (e.g., a band index, an absoluteradio frequency channel number (ARFCN)) and a cell ID (e.g., a physicalcell ID (PCI)) of a candidate cell, may be generated by concatenatingthe PCI of the candidate cell and an ID of a target node related to thecandidate cell, or may be generated by concatenating the frequencyinformation, the ID of the target node related to the candidate cell,and the PCI of the candidate cell. In this case, in order to determinewhether to store the candidate cell ID and/or the candidate cellconfiguration related thereto, a UE may compare concatenated values of acandidate cell ID given in an RRC reconfiguration message withconcatenated values of the candidate cell ID stored in the UE,respectively, and if all the compared values are the same, the UE maydetermine that the candidate cell ID stored in the UE and the candidatecell ID in the RRC reconfiguration message are the same.

In another embodiment, a serving node may assign any one integer valueas a CHO candidate cell ID, on the basis of the cell ID, the target nodeID, and the frequency information.

In various embodiments, a cell group ID (CGI) value may be used as acandidate cell ID. If the candidate cell ID is generated based on thePCI and ARFCN, when the UE releases the candidate cell, the UE mayrelease a configuration of a candidate cell in which the concatenationof the cell ID and the ARFCN matches. According to an embodiment, if aPCI value is indicated to the UE, the UE may release any candidate cellcorresponding to the indicated PCI value, regardless of an ARFCN value.According to another embodiment, if an ARFCN value is indicated to theUE, the UE may not release any candidate cell corresponding to theindicated ARFCN value, regardless of an PCI value.

In various embodiments, if a candidate cell ID is generated based on thePCI and the target node ID, when the UE releases the candidate cell, theUE may release a configuration of a candidate cell in which theconcatenation of the PCI and the target node ID matches. According to anembodiment, if a PCI value is indicated to the UE, the UE may releaseany candidate cell corresponding to the indicated PCI value, regardlessof a target node ID value. According to another embodiment, if a targetnode ID value is indicated to the UE, the UE may not release anycandidate cell corresponding to the indicated target node ID value,regardless of a PCI value.

In various embodiments, a candidate cell ID may be generated based on aconcatenation of the PCI and the ARFCN, a concatenation of the PCI andthe target node ID, or a concatenation of the PCI, the ARFCN and thetarget node ID. In this case, the serving node may generate a randominteger corresponding to each concatenated PCI, ARFCN and/or target nodeID. The serving node may determine a total size of the candidate cell IDand may determine a size of a bit stream, which corresponds to each PCI,ARFCN and/or target node ID, for a hard split. For example, if each of abit size of the PCI, a bit size of the ARFCN, and a bit size of thetarget node ID is defined as 5:5:5, one random integer value assignedfrom a PCI ID may be represented as a bit stream in first 5 bits, onerandom integer value assigned from the ARFCN may be represented as a bitstream in middle 5 bits, and one random integer value based on thetarget node ID may be represented as a bit stream in last 5 bits. Forexample, if each of the PCI, ARFCN, and target node ID has integervalues of 2:5:3, the bit streams may be displayed as a concatenation of00010:00101:00011.

In various embodiments, for each concatenation, when a base stationtransmits a release signal to the UE, if each of the PCI, ARFCN, andtarget node ID or the integer values thereof are provided, the UE mayrelease a candidate cell of any candidate cell ID including the providedID.

In the FIG. 9, a number of entities and various operations of eachentity are described, but these are only mentioned to faithfullydescribe the handover process. That is, it does do not mean that aspecific entity must need to perform all of the operations of thespecific entity illustrated in FIG. 9. Some operations may be omitted ormay be performed intermittently in describing certain embodiments of thepresent disclosure. For example, steps 915 to 923 may be omitted.

FIG. 10 illustrates an example of a case in which a serving node assignsa CHO candidate cell ID and then transmits a handover request message toa target node in the wireless communication system according to variousembodiments. In FIG. 10, a UE 1010 may be the terminal 120, and aserving node 1020 may be the base station 110. Each of target node 11030 and target node 2 1040 may have the elements of the base station110 illustrated in FIG. 2.

Referring to FIG. 10, in operation 1001, the UE 1010 may receive ameasurement configuration from the serving node 1020. For example, theUE 1010 may be connected to a serving cell and may receive a measurementconfiguration from the serving node 1020 related to the serving cell.

In operation 1003, the UE 1010 may transmit a measurement report to theserving node 1020. The UE 1010 may perform measurement based on themeasurement configuration and may transmit the measurement reportincluding a measurement result to the serving node 1020.

In operation 1005, the serving node 1020 may assign a CHO candidate cellID on the basis of a node ID and a cell ID for cell 1 of target node 11030. For example, the serving node 1020 may assign a CHO candidate cellID by using information related to an ID of target node 1 1030 and/orinformation related to an ID of a target cell (e.g., cell 1). The CHOcandidate cell ID assigned in operation 1005 may be an ID for cell 1 ofthe target node 1 1030. In other words, unlike in FIG. 9, the servingnode 1020 may assign a candidate cell ID before transmitting a handoverrequest message.

In operation 1007, the serving node 1020 may transmit a HANDOVER REQUESTmessage to target node 1 1030. For example, the serving node 1020 maytransmit the HANDOVER REQUEST message for requesting a CHO to targetnode 1 1030 related to at least one cell, on the basis of themeasurement result. In various embodiments, the HANDOVER REQUEST messagemay include handover (HO) preparation information. The HANDOVER REQUESTmessage may further include a candidate cell ID for cell 1 of targetnode 1 1030.

In operation 1009, target node 1 1030 may transmit a handover requestacknowledgment (ACK) message to the serving node 1020. Target node 11030 may reserve a resource to be used by the UE 1010 and may transmitthe HANDOVER REQUEST ACK message including CHO configuration informationfor cell 1 of target node 1 1030 to the serving node 1020. The HANDOVERREQUEST ACK message may further include the candidate cell ID for cell 1of target node 1 1030. In various embodiments, the candidate cell ID forcell 1 may be included in the CHO configuration information for cell 1.

In operation 1011, the serving node 1020 may transmit an RRCreconfiguration message to the UE 1010. The RRC reconfiguration messageof operation 1011 may include a list of one or more candidate cellconfigurations, and each candidate cell configuration may include acandidate cell ID and a CHO configuration for each candidate cellincluding a CHO trigger condition. In various embodiments, the list ofcandidate cell configurations may be referred to as “AddModlist”. Invarious embodiments, for the list of candidate cell configurations, theUE 1010 may, based on a candidate cell ID, i) correct a candidate cellconfiguration for a candidate cell ID which the UE 1010 already has, andii) enable a candidate cell configuration for a candidate cell ID, whichthe UE 1010 does not have, to be stored in the UE 1010.

In operation 1013, the UE 1010 may determine whether a candidate cell IDstored in the UE 1010 exists in the received list. If the candidate cellID stored in the UE 1010 exists in the received list, the UE 1010 mayupdate a CHO configuration and a CHO trigger condition for the candidatecell ID stored in the UE 1010, with a CHO configuration and a CHOtrigger condition for the corresponding candidate cell ID in the list ofreceived candidate cell configurations. In other words, if the candidatecell ID stored in the UE 1010 exists in the received list, the UE 1010may update the candidate cell configuration related to the candidatecell ID stored in the UE 1010, with the received candidate cellconfiguration related to the corresponding candidate cell ID.

In various embodiments, for the list received from the serving node 1020may include: i) all candidate cell configurations for all candidatecells regardless of candidate cell configurations to be changed; ii)candidate cell configurations to be changed based on the configurationof the UE 1010 currently used in the serving cell; or iii) candidatecell configurations changed based on previously transmitted candidatecell configurations. When the UE 1010 updates the candidate cellconfiguration, if the candidate cell ID stored in the UE 1010 exists inthe received list, the following operations of A), B) or C) may beperformed for the cases of i), ii), and iii), respectively. A) The UE1010 may delete the candidate cell configuration for the correspondingcandidate cell ID stored in the UE 1010 and may store the receivedcandidate cell configuration related to the corresponding candidate cellID. B) With respect to the candidate cell configuration for thecorresponding candidate cell ID stored in the UE 1010, the UE 1010 maychange, to the received configuration information, configurationinformation different from the candidate cell configuration related tothe currently stored corresponding candidate cell ID in comparison withthe configuration updated to the received candidate cell configurationon the basis of the configuration of the UE being used in the currentserving cell, or the UE 910 may newly add and store the receivedconfiguration information. C) The UE 1010 may change, to the receivedconfiguration information, configuration information different from thecurrently received candidate cell configuration among previouslyreceived candidate cell configurations, or may newly add and store thereceived configuration information.

If a candidate cell configuration having a candidate cell ID differingfrom the candidate cell ID stored in the UE 1010 exists in the list ofthe candidate cell configurations received from the serving node 1020,the UE 1010 may store a candidate cell configuration for a new candidatecell ID (e.g., a CHO configuration and a CHO trigger condition), mayperform measurement on a new candidate cell on the basis of thecandidate cell configuration, and may evaluate whether a CHO triggercondition for the new candidate cell is satisfied.

In operation 1015, the serving node 1020 may assign a CHO candidate cellID on the basis of a node ID and a cell ID for cell 2 of target node 21040. For example, the serving node 1020 may assign a CHO candidate cellID by using information related to an ID of target node 2 1040 and/orinformation related to an ID of a target cell (e.g., cell 2). The CHOcandidate cell ID assigned in operation 1015 may be an ID for cell 2 ofthe target node 2 1040. In other words, unlike in FIG. 9, the servingnode 1020 may assign a candidate cell ID before transmitting a handoverrequest message.

In operation 1017, the serving node 1020 may transmit a HANDOVER REQUESTmessage to target node 2 1040. For example, the serving node 1020 maytransmit the HANDOVER REQUEST message for requesting a CHO to targetnode 2 1040 related to at least one cell, on the basis of themeasurement result. In various embodiments, the HANDOVER REQUEST messagemay include handover (HO) preparation information. The HANDOVER REQUESTmessage may further include a candidate cell ID for cell 2 of targetnode 2 1040.

In operation 1019, target node 2 1040 may transmit a handover requestacknowledgment (ACK) message to the serving node 1020. Target node 21040 may reserve a resource to be used by the UE 1010 and may transmitthe HANDOVER REQUEST ACK message including CHO configuration informationfor cell 2 of target node 2 1040 to the serving node 1020. The HANDOVERREQUEST ACK message may further include the candidate cell ID for cell 2of target node 2 1040. In various embodiments, the candidate cell ID forcell 2 may be included in the CHO configuration information for cell 2.

In operation 1011, the serving node 1020 may transmit an RRCreconfiguration message to the UE 1010. The RRC reconfiguration messageof operation 1011 may include a list of one or more candidate cellconfigurations, and each candidate cell configuration may include acandidate cell ID and a CHO configuration for each candidate cellincluding a CHO trigger condition. In various embodiments, the list ofcandidate cell configurations may be referred to as “AddModlist”.

In operation 1013, the UE 1010 may determine whether a candidate cell IDstored in the UE 1010 exists in the received list. If the candidate cellID stored in the UE 1010 exists in the received list, the UE 1010 mayupdate a CHO configuration and a CHO trigger condition for the candidatecell ID stored in the UE 1010, with a CHO configuration and a CHOtrigger condition for the corresponding candidate cell ID in the list ofreceived candidate cell configurations. In other words, if the candidatecell ID stored in the UE 1010 exists in the received list, the UE 1010may update the candidate cell configuration related to the candidatecell ID stored in the UE 1010, with the received candidate cellconfiguration related to the corresponding candidate cell ID.

In various embodiments, for the list received from the serving node 1020may include: i) all candidate cell configurations for all candidatecells regardless of candidate cell configurations to be changed; ii)candidate cell configurations to be changed based on the configurationof the UE 1010 currently used in the serving cell; or iii) candidatecell configurations changed based on previously transmitted candidatecell configurations. When the UE 1010 updates the candidate cellconfiguration, if the candidate cell ID stored in the UE 1010 exists inthe received list, the following operations of A), B) or C) may beperformed for the cases of i), ii), and iii), respectively. A) The UE1010 may delete the candidate cell configuration for the correspondingcandidate cell ID stored in the UE 1010 and may store the receivedcandidate cell configuration related to the corresponding candidate cellID. B) With respect to the candidate cell configuration for thecorresponding candidate cell ID stored in the UE 1010, the UE 1010 maychange, to the received configuration information, configurationinformation different from the candidate cell configuration related tothe currently stored corresponding candidate cell ID in comparison withthe configuration updated to the received candidate cell configurationon the basis of the configuration of the UE being used in the currentserving cell, or the UE 910 may newly add and store the receivedconfiguration information. C) The UE 1010 may change, to the receivedconfiguration information, configuration information different from thecurrently received candidate cell configuration among previouslyreceived candidate cell configurations, or may newly add and store thereceived configuration information.

If a candidate cell configuration having a candidate cell ID differingfrom the candidate cell ID stored in the UE 1010 exists in the list ofthe candidate cell configurations received from the serving node 1020,the UE 1010 may store a candidate cell configuration for a new candidatecell ID (e.g., a CHO configuration and a CHO trigger condition), mayperform measurement on a new candidate cell on the basis of thecandidate cell configuration, and may evaluate whether a CHO triggercondition for the new candidate cell is satisfied.

In the FIG. 10, a number of entities and various operations of eachentity are described, but these are only mentioned to faithfullydescribe the handover process. That is, it does do not mean that aspecific entity must need to perform all of the operations of thespecific entity illustrated in FIG. 10. Some operations may be omittedor may be performed intermittently in describing certain embodiments ofthe present disclosure.

FIG. 11 illustrates an example of a case of modifying a candidate cellconfiguration by using a candidate cell ID in the wireless communicationsystem according to various embodiments. In FIG. 11, a UE 1110 may bethe terminal 120, and a serving node 1120 may be the base station 110.Each of target node 1 1130 and target node 2 1140 may have the elementsof the base station 110 illustrated in FIG. 2.

Referring to FIG. 11, in operation 1101, target node 1 1130 detects thata CHO configuration for a candidate target cell has been changed. Thecandidate target cell may be cell 1 of target node 1 1130. If a resourceconfiguration for a previously reserved resource is changed, target node1 1130 may identify a UE to which a corresponding resource is assignedand a serving node of the UE. In an example of FIG. 11, the UE to whichthe corresponding resource is assigned and the serving node of the UEmay be the UE 1110 and the serving node 1120, respectively.

In operation 1103, target node 1 1130 may transmit a HANDOVER REQUESTACK message or a CHO configuration update request message to the servingnode 1120. In various embodiments, the HANDOVER REQUEST ACK message orthe CHO configuration update request message may include a handover (HO)command, and the HO command may include a CHO configuration for cell 1,which includes a changed resource configuration. Furthermore, theHANDOVER REQUEST ACK message or the CHO configuration update requestmessage may include a candidate cell ID related to the changed CHOconfiguration (in the example of FIG. 11, the candidate cell ID for cell1). In other words, in operation 1103, target node 1 1130 may transmitinformation including at least one of the CHO configuration for cell 1including the changed resource configuration or the candidate cell IDrelated to the changed CHO configuration to the serving node 1120, andthe information may be transmitted via a HANDVOER REQUEST message orother message.

In operation 1105, the serving node 1120 may identify the candidate cellID related to the changed CHO configuration, based on the cell ID andnode ID for cell 1 of target node 1 1130. The serving node 1120 mayidentify the candidate cell ID of the candidate cell, the CHOconfiguration of which has been changed, and the changed CHOconfiguration.

In operation 1117, the serving node 1120 may transmit an RRCreconfiguration message to the UE 1110. The RRC reconfiguration messagemay include a list of one or more candidate cell configurations, andeach candidate cell configuration may include a candidate cell IDrelated to a changed CHO configuration, the changed CHO configuration,and/or a CHO trigger condition for a candidate cell of the candidatecell ID.

In operation 1109, the UE 1110 may determine whether a candidate cell IDstored in the UE 1110 exists in a received list. For example, the UE1110 may compare a candidate cell ID stored in the UE 1110 with thereceived list to determine whether a candidate cell configuration havingthe same candidate cell ID is identified. If a candidate cellconfiguration having the same candidate cell ID is identified, the UE1110 may identify a CHO trigger condition and/or a CHO configurationdifferent from the candidate cell configuration pre-stored in the UE1110, in the received candidate cell configuration for the correspondingcandidate cell ID, may update the pre-stored candidate cellconfiguration for the corresponding candidate cell ID with theidentified CHO configuration and/or CHO trigger condition, and may storethe updated CHO configuration and/or CHO trigger condition. Furthermore,the UE 1110 may perform measurement for the candidate cell on the basisof the updated candidate cell configuration and may evaluate whether theCHO trigger condition for the candidate cell is satisfied.

In the FIG. 11, a number of entities and various operations of eachentity are described, but these are only mentioned to faithfullydescribe the handover process. That is, it does do not mean that aspecific entity must need to perform all of the operations of thespecific entity illustrated in FIG. 11. Some operations may be omittedor may be performed intermittently in describing certain embodiments ofthe present disclosure.

FIG. 12 illustrates an example of a case of releasing a candidate cellconfiguration on the basis of a candidate cell ID in the wirelesscommunication system according to various embodiments. In FIG. 12, a UE1210 may be the terminal 120, and a serving node 1220 may be the basestation 110. Each of target node 1 1230 and target node 2 1240 may havethe elements of the base station 110 illustrated in FIG. 2. In FIG. 12,it is assumed that a CHO candidate cell configuration for a candidatetarget cell has been previously transferred to the UE 1210.

Referring to FIG. 12, in operation 1201, target node 1 1230 may transmita HANDOVER REQUEST negative ACK (NACK) message or a message forrequesting release of a preconfigured HO configuration to the servingnode 1220. For example, in response to reception of a HANDOVER REQUESTmessage from the serving node 1220, target node 1 1230 may transmit, tothe serving node 1220, the HANDOVER REQUEST NACK message including acandidate cell ID or a cell group identifier (CGI) or a message forrequesting release of the preconfigured HO configuration. When theHANDOVER REQUEST NACK message or the message for requesting release ofthe preconfigured HO configuration and/or a handover cancellationcommand are received from target node 1 1230, the serving node 1220 mayrelease a candidate cell configuration for a received candidate cell ID.

In operation 1203, the serving node 1220 may detect expiration of avalidity timer for a candidate cell of target node 1 1230. In variousembodiments, the validity timer may count a time when resourceassignment for a candidate cell for a CHO is valid. If the expiration ofthe validity timer for the candidate cell is detected, the serving node1220 may release the candidate cell configuration for the candidatecell.

In various embodiments, operations 1201 and 1203 may be selectivelyperformed. In this case, operation 1201 or operation 1203 may beomitted.

In operation 1205, the serving node 1220 may identify a candidate cellID related to a CHO configuration to be released when a CHO candidatecell ID is already configured to the UE 1210, on the basis of a cell IDand a node ID. In other words, the serving node 1220 may identify thecandidate cell ID related to the candidate cell configuration to bereleased.

In operation 1207, the serving node 1220 may transmit an RRCreconfiguration message to the UE 1210. In various embodiments, the RRCreconfiguration message may include a release field including a list ofone or more candidate cell IDs for one or more candidate cellconfigurations to be released. In other words, the serving node 1220 maytransmit, to the UE 1210, information including a candidate cell IDrelated to a candidate cell configuration to be released and anindicator indicating to release the candidate cell configuration for thecandidate cell ID.

In operation 1209, the UE 1210 may release CHO configurations forcandidate cells of the cell ID included in the release field. The UE1210 may stop measurement for evaluating a CHO trigger condition and aCHO trigger condition of the released candidate cell, and may releasethe candidate cell configuration. In other words, the UE 1210 mayrelease one or more candidate cell configurations for the received oneor more candidate cell IDs.

In the FIG. 12, a number of entities and various operations of eachentity are described, but these are only mentioned to faithfullydescribe the handover process. That is, it does do not mean that aspecific entity must need to perform all of the operations of thespecific entity illustrated in FIG. 12. Some operations may be omittedor may be performed intermittently in describing certain embodiments ofthe present disclosure.

FIG. 13 illustrates an example of a case of releasing a candidate cellconfiguration when a CHO is performed in the wireless communicationsystem according to various embodiments. In FIG. 13, a UE 1310 may bethe terminal 120, and a serving node 1320 may be the base station 110.Target node 1330 may have the configurations of the base station 110illustrated in FIG. 2.

Referring to FIG. 13, in operation 1301, the serving node 1320 maytransmit an HO request message including a CHO indication to target node1330. In various embodiments, the CHO indication may indicate, to thetarget node, that the HO request is a request for a CHO.

In operation 1303, the target node 1330 may transmit an HO requestmessage ACK message to the serving node 1320. In various embodiments,the HO request message ACK may include one or more CHO configurationsfor one or more candidate cells of the target node 1330 for CHO.Furthermore, the HO request message ACK may include one or more CHOtrigger conditions for one or more candidate cells of the target node1330 for CHO.

In operation 1305, the serving node 1320 may assign a candidate cell ID.For example, the serving node 1320 may assign a candidate cell ID forthe candidate cell, on the basis of a target node ID and/or a cell ID inthe CHO configuration received in operation 1303.

In operation 1307, the serving node 1320 may transmit an RRCreconfiguration message to the UE 1310. The RRC reconfiguration messagemay include a list of one or more candidate cell configurations, andeach candidate cell configuration may include a candidate cell ID, and aCHO configuration and a CHO trigger condition for the candidate cell ID,which are received from the target node 1330.

In operation 1309, the UE 1310 may add, to a list of the UE 1310,candidate cell configurations related to candidate cell IDs that are notstored in the UE 1310 from the received list of candidate cellconfigurations, and may perform, based on the candidate cellconfigurations, measurement for candidate cells of correspondingcandidate cell IDs.

In operation 1311, the UE 1310 may determine a candidate target cellthat satisfies the CHO trigger condition, and may perform a CHO for thedetermined candidate target cell. More specifically, as a result of themeasurement in operation 1309, if the CHO trigger condition is satisfiedfor one or more candidate cells at a specific time point, the UE 1310may select one target cell from among the one or more candidate cells,for which the condition is satisfied, and may perform the CHO to theselected target cell. In this case, the UE 1310 may perform the CHO to atarget cell by applying the candidate cell configuration for the targetcell, and may release candidate cell configurations (e.g., CHOconfigurations and CHO trigger conditions) for candidate cells otherthan the target cell.

In operation 1313, the UE 1310 may transmit a random access preamble tothe target cell of the target node 1330. The UE 1310 may initiate arandom access procedure by transmitting the random access preamble tothe target cell to establish uplink synchronization for the target cell.

In the FIG. 13, a number of entities and various operations of eachentity are described, but these are only mentioned to faithfullydescribe the handover process. That is, it does do not mean that aspecific entity must need to perform all of the operations of thespecific entity illustrated in FIG. 13. Some operations may be omittedor may be performed intermittently in describing certain embodiments ofthe present disclosure.

FIG. 14 illustrates an example of a case of releasing a candidate cellconfiguration after a CHO is successfully performed in the wirelesscommunication system according to various embodiments. In FIG. 14, a UE1410 may be the terminal 120, and a serving node 1420 may be the basestation 110. Target node 1430 may have the configurations of the basestation 110 illustrated in FIG. 2.

Referring to FIG. 14, in operation 1401, the serving node 1420 maytransmit an HO request message including a CHO indication to the targetnode 1430. In various embodiments, the CHO indication may include anindicator indicating that a CHO will be performed.

In operation 1403, the target node 1430 may transmit an HO requestmessage ACK message to the serving node 1420. In various embodiments,the HO request message ACK may include one or more CHO configurationsfor one or more candidate cells of the target node 1430 for CHO.Furthermore, the HO request message ACK may include one or more CHOtrigger conditions for one or more candidate cells of the target node1430 for CHO.

In operation 1405, the serving node 1420 may assign a candidate cell ID.For example, the serving node 1420 may assign a candidate cell ID forthe candidate cell, on the basis of a target node ID and/or a cell ID inthe CHO configuration received in operation 1403.

In operation 1407, the serving node 1420 may transmit an RRCreconfiguration message to the UE 1410. The RRC reconfiguration messagemay include a list of one or more candidate cell configurations, andeach candidate cell configuration may include a candidate cell ID, and aCHO configuration and a CHO trigger condition for the candidate cell ID,which are received from the target node 1430.

In operation 1409, the UE 1410 may add, to a list of the UE 1410,candidate cell configurations related to candidate cell IDs that are notstored in the UE 1410 from the received list of candidate cellconfigurations, and may perform, based on the candidate cellconfigurations, measurement for candidate cells of correspondingcandidate cell IDs. As a result of the measurement, if the CHO triggercondition is satisfied for one or more candidate cells at a specifictime point, the UE 1410 may select one target cell from among the one ormore candidate cells, for which the condition is satisfied, and mayperform the CHO to the selected target cell. In this case, the UE 1410may perform the CHO to the target cell by applying a candidate cellconfiguration for the target cell.

In operation 1411, the UE 1410 may transmit a random access preamble tothe target cell of the target node 1430. The UE 1410 may initiate arandom access procedure by transmitting the random access preamble tothe target cell to establish uplink synchronization for the target cell.

In operation 1413, the target node 1430 may transmit a random accessresponse (RAR) message to the UE 1410. The RAR message may include arandom access preamble detected by the target node 1430 and an uplinkgrant (UL grant).

In operation 1415, the UE 1410 may transmit an HO completion or RRCreconfiguration completion (RRCReconfigurationComplete) message to thetarget node 1430. After completing the handover to the target node 1430,the UE 1410 may transmit the HO completion or RRC reconfigurationcompletion (RRCReconfigurationComplete) message to the target node 1430.

In operation 1417, the UE 1410 may release some or all of CHO candidatecell configurations for the remaining candidate cells other than thetarget cell for which that handover has been successful. Morespecifically, if the CHO to the target cell by the UE 1410 issuccessful, the UE 1410 may release some or all of the CHO candidatecell configurations for the remaining candidate cells other than thetarget cell for which the CHO has been successful. In variousembodiments, the success of a handover may correspond to transmission ofan RRC reconfiguration completion (RRCReconfigurationComplete) message.

In the FIG. 14, a number of entities and various operations of eachentity are described, but these are only mentioned to faithfullydescribe the handover process. That is, it does do not mean that aspecific entity must need to perform all of the operations of thespecific entity illustrated in FIG. 14. Some operations may be omittedor may be performed intermittently in describing certain embodiments ofthe present disclosure.

According to embodiments, a method performed by a user equipment (UE) ina wireless communication system, the method comprises: receiving, from abase station, a radio resource control (RRC) reconfiguration messageincluding conditional configuration information, and a configuration ofthe candidate cell; and performing one or more operations for aconditional handover based on RRC reconfiguration message. Theconditional configuration information includes: identificationinformation for a candidate cell.

In some embodiments, the conditional configuration information furtherincludes information on a condition for triggering an execution of theconfiguration of the candidate cell, and the performing of the one ormore operations for the conditional handover comprises evaluating thecondition.

In some embodiments, the performing of the one or more operations forthe conditional handover comprises: based on identifying that thecondition is met based on a measurement result, applying the conditionalconfiguration.

In some embodiments, the method further comprises identifying whetherthe identification information for the candidate cell exists in a liststored in the UE; and if the identification information for thecandidate cell does not exist in a list stored in the UE, storing theconditional configuration information.

In some embodiments, the method further comprises, if the identificationinformation for the candidate cell exists in the list stored of the UE,replacing one configuration of the candidate cell stored in the UE withthe received configuration of the candidate cell.

In some embodiments, the method further comprises, if the identificationinformation for the candidate cell exists in the list stored of the UE,replacing one condition of the candidate cell stored in the UE with acondition for triggering an execution of the configuration of thecandidate cell. The conditional configuration information furtherincludes information on the condition.

In some embodiments, the method further comprises, receiving, from thebase station, an RRC reconfiguration message including information on arelease list including identification information for another candidatecell; if the identification information for another candidate cellexists in the list stored of the UE, releasing a conditionalconfiguration corresponding to the identification information foranother candidate cell.

In some embodiments, the RRC reconfiguration message includes anaddition/modification list for one or more conditional configurationinformation, and the addition/modification list includes the conditionalconfiguration information.

According to embodiments, a method performed by a base station in awireless communication system, comprises generating a radio resourcecontrol (RRC) reconfiguration message including conditionalconfiguration information, wherein the conditional configurationinformation includes: identification information for a candidate cell;and a configuration of the candidate cell; and transmitting, to a userequipment (UE), a radio resource control (RRC) reconfiguration messagefor a conditional handover.

In some embodiments, the conditional configuration information furtherincludes information on a condition for triggering an execution of theconfiguration of the candidate cell.

In some embodiments, the method further comprises, before generating theRRC reconfiguration message, transmitting, to a target base stationproviding the candidate cell, a handover request message, and beforegenerating the RRC reconfiguration message, receiving, from the targetbase station, a handover request acknowledge message including theconfiguration of the candidate cell.

In some embodiments, the method further comprises: transmitting, to theUE, an RRC reconfiguration message including information on a releaselist including identification information for another candidate cell. Aconditional configuration corresponding to the identificationinformation for another candidate cell is released.

According to embodiments, a user equipment (UE) in a wirelesscommunication system, comprising: at least one transceiver; and at leastone processor configured to: receive, from a base station via the atleast one transceiver, a radio resource control (RRC) reconfigurationmessage including conditional configuration information; and perform oneor more operations for a conditional handover based on RRCreconfiguration message. The conditional configuration informationincludes: identification information for a candidate cell; and aconfiguration of the candidate cell.

In some embodiments, the conditional configuration information furtherincludes information on a condition for triggering an execution of theconfiguration of the candidate cell, and the performing of the one ormore operations for the conditional handover comprises evaluating thecondition.

In some embodiments, the at least one processor is, in order to performthe one or more operations for the conditional handover, configured to,based on identifying that the condition is met based on a measurementresult, apply the conditional configuration.

In some embodiments, the at least one processor is further configured toidentify whether the identification information for the candidate cellexists in a list stored in the UE; and if the identification informationfor the candidate cell does not exist in a list stored in the UE, storethe conditional configuration information.

In some embodiments, the at least one processor is further configuredto, if the identification information for the candidate cell exists inthe list stored of the UE, replace one configuration of the candidatecell stored in the UE with the received configuration of the candidatecell.

In some embodiments, the at least one processor is further configuredto, if the identification information for the candidate cell exists inthe list stored of the UE, replace one condition of the candidate cellstored in the UE with a condition for triggering an execution of theconfiguration of the candidate cell. The conditional configurationinformation further includes information on the condition.

In some embodiments, the at least one processor is further configured toreceive, from the base station via the at least one transceiver, an RRCreconfiguration message including information on a release listincluding identification information for another candidate cell; and ifthe identification information for another candidate cell exists in thelist stored of the UE, release a conditional configuration correspondingto the identification information for another candidate cell.

In some embodiments, the RRC reconfiguration message includes anaddition/modification list for one or more conditional configurationinformation, and the addition/modification list includes the conditionalconfiguration information.

According to embodiments, a base station in a wireless communicationsystem, comprises at least one transceiver; and at least one processorconfigured to generate a radio resource control (RRC) reconfigurationmessage including conditional configuration information, wherein theconditional configuration information includes: identificationinformation for a candidate cell; and a configuration of the candidatecell; and transmit, to a user equipment (UE) via the at least onetransceiver, a radio resource control (RRC) reconfiguration message fora conditional handover.

In some embodiments, the conditional configuration information furtherincludes information on a condition for triggering an execution of theconfiguration of the candidate cell.

In some embodiments, the at least one processor is, before generatingthe RRC reconfiguration message, further configured to: transmit, to atarget base station providing the candidate cell via the at least onetransceiver, a handover request message, and receive, from the targetbase station via the at least one transceiver, a handover requestacknowledge message including the configuration of the candidate cell.

In some embodiments, the at least one processor is further configuredto: transmit, to the UE via the at least one transceiver, an RRCreconfiguration message including information on a release listincluding identification information for another candidate cell. Aconditional configuration corresponding to the identificationinformation for another candidate cell is released.

According to embodiments, an operation method of a terminal in awireless communication system, the method comprises receiving candidatecell configurations for one or more candidate cells for a conditionalhandover (CHO) from a base station; identifying a candidate cellidentifier (ID) for each candidate cell in the candidate cellconfigurations; and based on the candidate cell ID, updating a candidatecell configuration corresponding to the candidate cell ID to a list ofcandidate cell configurations, which is stored in the terminal, whereinthe candidate cell ID may be generated based on at least one of an ID ofthe base station or a cell ID of a candidate cell.

In some embodiments, the updating of the candidate cell configurationcomprises: if the candidate cell ID is included in the list of candidatecell configurations, which is stored in the terminal, updating acandidate cell configuration related to the candidate cell ID in thelist of candidate cell configurations stored in the terminal by using acandidate cell configuration received from the base station.

In some embodiments, the updating of the candidate cell configurationcomprises: if the candidate cell ID is not included in the list ofcandidate cell configurations, which is stored in the terminal, addingthe received candidate cell configurations to the list of candidate cellconfigurations stored in the terminal; based on the candidate cellconfigurations, performing measurement for a candidate cell of thecandidate cell ID; and performing a handover to the candidate cell inresponse to that a result of the measurement satisfies a CHO triggercondition.

According to embodiments, an operation method of a base station in awireless communication system, the method comprises based on at leastone of an identifier (ID) of the base station or a cell ID of acandidate cell for a conditional handover (CHO), generating a candidatecell ID of the candidate cell; and transmitting, to a terminal, acandidate cell configuration comprising at least one of the candidatecell ID, a CHO configuration, or a CHO trigger condition, wherein atleast one of the CHO configuration or the CHO trigger condition isreceived from an adjacent base station related to the candidate cell viaa handover acknowledgment message for a handover request.

In some embodiments, the method further comprises: before generating thecandidate cell ID, transmitting the handover request to the adjacentbase station; and receiving the handover acknowledgment messagecomprising the CHO configuration from the adjacent base station.

In some embodiments, the method further comprises: transmitting thehandover request comprising the candidate cell ID to the adjacent basestation; and receiving the CHO configuration comprising the candidatecell ID from the adjacent base station via the handover acknowledgmentmessage.

According to embodiments, a terminal in a wireless communication system,the terminal comprising: a transceiver configured to receive candidatecell configurations for one or more candidate cells for a conditionalhandover (CHO) from a base station; and at least one processorconfigured to identify a candidate cell identifier (ID) for eachcandidate cell in the candidate cell configurations, and update, basedon the candidate cell ID, a candidate cell configuration correspondingto the candidate cell ID to a list of candidate cell configurations,which is stored in the terminal, wherein the candidate cell ID isgenerated based on at least one of an ID of the base station or a cellID of a candidate cell.

In some embodiments, the at least one processor is configured to, if thecandidate cell ID is included in the list of candidate cellconfigurations, which is stored in the terminal, update a candidate cellconfiguration related to the candidate cell ID in the list of candidatecell configurations stored in the terminal by using a candidate cellconfiguration received from the base station.

In some embodiments, the at least one processor is configured to: if thecandidate cell ID is not included in the list of candidate cellconfigurations, which is stored in the terminal, add the receivedcandidate cell configurations to the list of candidate cellconfigurations stored in the terminal; based on the candidate cellconfigurations, perform measurement for a candidate cell of thecandidate cell ID; and perform a handover to the candidate cell inresponse to that a result of the measurement satisfies a CHO triggercondition.

FIG. 15 illustrates an example of a case of performing an applicabilitycheck in the wireless communication system according to variousembodiments. In FIG. 15, a UE 1510 may be the terminal 120, and anetwork 1520 may include at least one base station (e.g., the basestation 110). Each base station may have the configurations of the basestation 110 illustrated in FIG. 2.

Referring to FIG. 15, in operation 1501, the UE 1510 may receive an RRCreconfiguration (RRCReconfiguration) message from the network 1520. TheRRC reconfiguration message may include information for reconfiguration.

In operation 1503, the UE 1510 may determine whether receivedconfiguration information is applicable. In other words, the UE 1510 mayperform an applicability check for the received reconfigurationinformation. The UE 1510 may determine whether the receivedreconfiguration information is applicable at a time point of applyingthe received reconfiguration information. If the reconfigurationinformation is applicable, the UE 1510 may perform operation 1505 oroperation 1507. If the reconfiguration information is not applicable,the UE 1510 may perform operation 1511, operation 1513, or operation1515.

In operation 1505, the UE 1510 may transmit an RRC reconfigurationcompletion (RRCReconfigurationComplete) message to the network 1520. Ifthe received reconfiguration information is applicable, the UE 1510 maytransmit the RRCReconfigurationComplete message to a source cell for aCHO.

In operation 1507, the UE 1510 may transmit theRRCReconfigurationComplete message to the network 1520. If the receivedreconfiguration information is applicable, and the UE 1510 receives aCHO command, the UE 1510 may transmit the RRCReconfigurationCompletemessage to a target cell for a Cho.

Operation 1505 and operation 1507 may be selectively performed. In otherwords, operation 1505 or operation 1507 may be omitted.

In operation 1509, the UE 1510 may apply a previous configuration. Inother words, as a result of the applicability check, if the UE 1510cannot apply all or a part of the received reconfiguration information,the UE 1510 may apply configuration information before reception of thereconfiguration information.

In operation 1511, the UE 1510 may perform an RRC connectionre-establishment (RRE) procedure. In a state in which the configurationinformation before reception of the reconfiguration information has beenapplied, the UE 1510 may perform the RRC connection re-establishmentprocedure.

In operation 1513, the UE 1510 may perform a secondary cell group (SCG)failure information procedure. For example, if configuration orreconfiguration information related to a primary secondary cell (PSCell)is not applicable, the UE 1510 may perform the SCG failure informationprocedure.

In operation 1515, the UE 1510 may transition to an RRC IDLE mode. Forexample, if access stratum (AS) security is not applied, the UE 1510 maytransition to the RRC IDLE mode.

Operations 1511, 1513, and 1515 may be selectively performed. In otherwords, one of operations 1511, 1513, and 1515 is performed, and theremaining operations may not be performed.

FIG. 16 illustrates an example of a case of, if an applicability checkfor a CHO candidate cell configuration is successful, transmitting anRRC reconfiguration completion message to a source cell in the wirelesscommunication system according to various embodiments. In FIG. 16, a UE1610 may be the terminal 120, and operations of a source cell 1620 and atarget cell 1630 may be performed by the elements of the base station110.

Referring to FIG. 16, in operation 1601, the source cell 1620 maytransmit a CHO request to the target cell 1630. The source cell 1620 mayrequest a CHO from the target cell 1630 via a CHO request.

In operation 1603, the target cell 1630 may transmit a CHO request ACKto the source cell 1620. The target cell 1630 may transmit, to thesource cell 1620, the CHO request ACK message to accept the CHO request.

In operation 1605, the source cell 1620 may transmit an RRCreconfiguration message to the UE 1610. The RRC reconfiguration messagemay include a candidate cell configuration for a candidate cell (e.g.,the target cell 1630), and the candidate cell configuration may includea CHO configuration, a CHO trigger condition, and a candidate targetcell ID for the candidate cell (e.g., the target cell 1630).

In operation 1607, the UE 1610 may determine whether the receivedcandidate cell configuration is applicable. In other words, the UE 1610may perform an applicability check for the received candidate cellconfiguration. In FIG. 16, it is assumed that the applicability check issuccessful.

In operation 1609, the UE 1610 may store the candidate cellconfiguration and may perform measurement to determine whether the CHOtrigger condition is satisfied.

In operation 1611, the UE 1610 may transmit anRRCReconfigurationComplete message to the source cell 1620,independently of operation 1609, in response to the success of theapplicability check. After applying the candidate cell configurationreceived from the source cell 1620, the UE 1610 may transmit theRRCReconfigurationComplete message to the source cell 1620.

FIG. 17 illustrates an example of a case of, if an applicability checkfor a CHO candidate cell configuration is successful, transmitting anRRC reconfiguration completion message to a target cell in the wirelesscommunication system according to various embodiments. In FIG. 17, a UE1710 may be the terminal 120, and operations of a source cell 1720 and atarget cell 1730 may be performed by the elements of the base station110.

Referring to FIG. 17, in operation 1701, the source cell 1720 maytransmit a CHO request to the target cell 1730. The source cell 1720 mayrequest a CHO from the target cell 1730 via a CHO request.

In operation 1703, the target cell 1730 may transmit a CHO request ACKto the source cell 1720. The target cell 1730 may transmit the CHOrequest ACK message for accepting of the CHO request to the source cell1720.

In operation 1705, the source cell 1720 may transmit an RRCreconfiguration message to the UE 1710. The RRC reconfiguration messagemay include a candidate cell configuration for a candidate cell (e.g.,the target cell 1730), and the candidate cell configuration may includea CHO configuration, a CHO trigger condition, and a candidate targetcell ID for the candidate cell (e.g., the target cell 1730).

In operation 1707, the UE 1710 may determine whether the receivedcandidate cell configuration is applicable. In other words, the UE 1710may perform an applicability check for the received candidate cellconfiguration. In FIG. 17, it is assumed that the applicability check issuccessful.

In operation 1709, the UE 1710 may store the candidate cellconfiguration and may perform measurement to determine whether the CHOtrigger condition is satisfied. If the CHO trigger condition issatisfied at a specific time point, the UE 1710 may perform a CHO to acandidate cell (e.g., the target cell 1730) related to the CHO triggercondition.

In operation 1711, the UE 1710 may transmit anRRCReconfigurationComplete message to the target cell 1730. If the CHOis successful, the UE 1710 may transmit a random access preamble, mayreceive an RAR, and may transmit the RRCReconfigurationComplete messageto the target cell 1730 via message3 or message5.

FIG. 18 illustrates an example of a case of, if an applicability checkfor a CHO candidate cell configuration has failed, transmitting afailure message in the wireless communication system according tovarious embodiments. In FIG. 18, a UE 1810 may be the terminal 120, andoperations of a source cell 1820 and a target cell 1830 may be performedby the elements of the base station 110.

Referring to FIG. 18, in operation 1801, the source cell 1820 maytransmit a CHO request to the target cell 1830. The source cell 1820 mayrequest a CHO from the target cell 1830 via a CHO request.

In operation 1803, the target cell 1830 may transmit a CHO request ACKto the source cell 1820. The target cell 1830 may transmit the CHOrequest ACK message for accepting of the CHO request to the source cell1820.

In operation 1805, the source cell 1820 may transmit an RRCreconfiguration message to the UE 1810. The RRC reconfiguration messagemay include a candidate cell configuration for a candidate cell (e.g.,the target cell 1830), and the candidate cell configuration may includea CHO configuration, a CHO trigger condition, and a candidate targetcell ID for the candidate cell (e.g., the target cell 1830).

In operation 1807, the UE 1810 may determine whether the receivedcandidate cell configuration is applicable. In other words, the UE 1810may perform an applicability check for the received candidate cellconfiguration. In FIG. 18, it is assumed that the applicability checkhas failed.

In operation 1809, the UE 1810 may transmit an RRC message including aCHO failure indication and a candidate cell ID to the source cell 1820.In other words, the UE 1810 may transmit the RRC message to the sourcecell 1820, the RRC message including an indicator indicating that theapplicability check for the CHO candidate cell configuration has failed,and the candidate cell ID related to the CHO candidate cellconfiguration.

In operation 1811, the source cell 1820 may transmit a CHO cancellationmessage or a new CHO request message to the target cell 1830. The sourcecell 1820 may transmit the new CHO request message to the target cell1830 that is a cell having the candidate cell ID related the CHOcandidate cell configuration, for which the applicability check hasfailed, or may transmit the CHO cancellation message.

FIG. 19 illustrates an example of a case of, if an applicability checkfor a CHO candidate cell configuration has failed, performing an RRCconnection re-establishment procedure in the wireless communicationsystem according to various embodiments. In FIG. 19, a UE 1910 may bethe terminal 120, and operations of a source cell 1920 and a target cell1930 may be performed by the elements of the base station 110.

Referring to FIG. 19, in operation 1901, the source cell 1920 maytransmit a CHO request to the target cell 1930. The source cell 1920 mayrequest a CHO from the target cell 1930 via a CHO request.

In operation 1903, the target cell 1930 may transmit a CHO request ACKto the source cell 1920. The target cell 1930 may transmit the CHOrequest ACK message for accepting of the CHO request to the source cell1920.

In operation 1905, the source cell 1920 may transmit an RRCreconfiguration message to the UE 1910. The RRC reconfiguration messagemay include a candidate cell configuration for a candidate cell (e.g.,the target cell 1930), and the candidate cell configuration may includea CHO configuration, a CHO trigger condition, and a candidate targetcell ID for the candidate cell (e.g., the target cell 1930).

In operation 1907, the UE 1910 may determine whether the receivedcandidate cell configuration is applicable. In other words, the UE 1910may perform an applicability check for the received candidate cellconfiguration. In FIG. 19, it is assumed that the applicability checkhas failed.

In operation 1909, the UE 1910 may apply a current configuration. Inother words, the UE 1910 may apply an RRC configuration that iscurrently being used by the UE 1910, without applying the received RRCreconfiguration (e.g., the candidate cell configuration for the targetcell 1930).

In operation 1911, the UE 1910 may perform aRRCConnectionRe-estabilishment procedure. For theRRCConnectionRe-estabilishment procedure, the UE 1910 may transmit anRRCConnectionRe-estabilishment request message to a selected cell 1940.For example, when AS security is enabled, the UE 1910 may transmit, forthe RRCConnectionRe-estabilishment procedure, theRRCConnectionRe-estabilishment request message to the selected cell 1940via a cell selection procedure.

In various embodiments, when the AS security is not enabled, the UE 1910may transition to an RRC IDLE state. In this case, operation 1911 may beomitted.

FIG. 20 illustrates an example of a case of, if an applicability checkfor a plurality of CHO candidate cell configurations is successful,transmitting an RRC reconfiguration completion message in the wirelesscommunication system according to various embodiments. In FIG. 20, a UE2010 may be the terminal 120, and operations of a source cell 2020 and atarget cell 2030 may be performed by the elements of the base station110.

Referring to FIG. 20, in operation 2001, the source cell 2020 maytransmit a CHO request to the target cell 2030. The source cell 2020 mayrequest a CHO from the target cell 2030 via a CHO request.

In operation 2003, the target cell 2030 may transmit a CHO request ACKto the source cell 2020. The target cell 2030 may transmit the CHOrequest ACK message for accepting of the CHO request to the source cell2020.

In operation 2005, the source cell 2020 may transmit an RRCreconfiguration message to the UE 2010. The RRC reconfiguration messagemay include a list of candidate cell configurations for a plurality ofcandidate cells, which includes a candidate cell configuration for acandidate cell (e.g., the target cell 2030), and each candidate cellconfiguration may include a candidate cell ID, a CHO configuration, anda CHO trigger condition for each candidate cell.

In operation 2007, the UE 2010 may determine whether each candidate cellconfiguration in the received list is applicable. In other words, the UE2010 may perform an applicability check for each candidate cellconfiguration. In FIG. 20, it is assumed that the applicability checkfor all candidate cell configurations of the received list issuccessful.

In operation 2009, the UE 2010 may transmit anRRCReconfigurationComplete message to the source cell 2020. In responseto determining that the applicability check for all candidate cellconfigurations has been successful, the UE 2010 may transmit theRRCReconfigurationComplete message to the source cell 2020.

In operation 2011, the UE 2010 may store candidate cell configurations,may perform measurement, and may evaluate CHO trigger conditions. The UE2010 may store candidate cell configurations, for which theapplicability check has been successful, may perform measurement foreach candidate cell on the basis of the CHO configuration for eachcandidate cell, and may determine whether the CHO trigger condition foreach candidate cell is satisfied, on the basis of a measurement result.

FIG. 21 illustrates an example of a case of, if an applicability checkfor a plurality of CHO candidate cell configurations is successful,performing a CHO and then transmitting an RRC reconfiguration completionmessage in the wireless communication system according to variousembodiments. In FIG. 21, a UE 2110 may be the terminal 120, andoperations of a source cell 2120 and a target cell 2130 may be performedby the elements of the base station 110.

Referring to FIG. 21, in operation 2101, the source cell 2120 maytransmit a CHO request to the target cell 2130. The source cell 2120 mayrequest a CHO from the target cell 2130 via a CHO request.

In operation 2103, the target cell 2130 may transmit a CHO request ACKto the source cell 2120. The target cell 2130 may transmit the CHOrequest ACK message for accepting of the CHO request to the source cell2120.

In operation 2105, the source cell 2120 may transmit an RRCreconfiguration message to the UE 2110. The RRC reconfiguration messagemay include a list of candidate cell configurations for a plurality ofcandidate cells, which includes a candidate cell configuration for acandidate cell (e.g., the target cell 2130), and each candidate cellconfiguration may include a candidate cell ID, a CHO configuration, anda CHO trigger condition for each candidate cell.

In operation 2107, the UE 2110 may determine whether each candidate cellconfiguration in the received list is applicable. In other words, the UE2110 may perform an applicability check for each candidate cellconfiguration. In FIG. 21, it is assumed that the applicability checkfor all candidate cell configurations of the received list issuccessful.

In operation 2109, the UE 2110 may store candidate cell configurations,for which the applicability check has been successful, may performmeasurement for each candidate cell, and may evaluate CHO triggerconditions. The UE 2110 may perform measurement for each candidate cellon the basis of the CHO configuration for each candidate cell, and maydetermine whether the CHO trigger condition for each candidate cell issatisfied, on the basis of a measurement result. If one or more CHOtrigger conditions are satisfied at a specific time point, the UE 2110may select a target cell from among candidate cells, for which the CHOtrigger condition is satisfied, and may perform a CHO to the selectedtarget cell.

In operation 2111, the UE 2110 may transmit anRRCReconfigurationComplete message to the target cell 2130. If the CHOis successful, the UE 2110 may transmit a random access preamble, mayreceive an RAR, and may transmit the RRCReconfigurationComplete messageto the target cell 2130 via message3 or message5.

FIG. 22 illustrates an example of a case of, if an applicability checkfor some candidate cell configurations among a plurality of CHOcandidate cell configurations has failed, transmitting a failure messagein the wireless communication system according to various embodiments.In FIG. 22, a UE 2210 may be the terminal 120, and operations of asource cell 2220, target cell 1 2230, and target cell 2 2240 may beperformed by the elements of the base station 110.

Referring to FIG. 22, in operation 2201, the source cell 2220 maytransmit a CHO request to the target cell 2230. The source cell 2220 mayrequest a CHO from the target cell 2230 via a CHO request.

In operation 2203, the target cell 2230 may transmit a CHO request ACKto the source cell 2220. The target cell 2230 may transmit, to thesource cell 2220, the CHO request ACK message to accept the CHO request.

In operation 2205, the source cell 2220 may transmit an RRCreconfiguration message to the UE 2210. The RRC reconfiguration messagemay include a list of candidate cell configurations for a plurality ofcandidate cells, which includes a candidate cell configuration for acandidate cell (e.g., the target cell 2230), and each candidate cellconfiguration may include a candidate cell ID, a CHO configuration, anda CHO trigger condition for each candidate cell.

In operation 2207, the UE 2210 may determine whether each candidate cellconfiguration in the received list is applicable. In other words, the UE2210 may perform an applicability check for each candidate cellconfiguration. In FIG. 22, it is assumed that the applicability checkfor some of the candidate cell configurations of the received listfails. For example, it is assumed that the candidate cell configurationfor target cell 1 2230 is not applicable, and the candidate cellconfiguration for target cell 2 2240 is applicable.

In operation 2209, the UE 2210 may transmit an RRC message to the sourcecell 2220. The RRC message may include CHO failure information, and theCHO failure information may include a candidate cell ID (e.g., thecandidate cell ID of target cell 1 2230) of a candidate cell, for whichthe candidate cell configuration is not applicable. As anotherembodiment, the RRC message may further include a candidate cell ID of acandidate cell (e.g., target cell 2 2240), for which the applicabilitycheck has been successful.

In operation 2211, the source cell 2220 may transmit a CHO cancellationmessage or a new CHO request message to target cell 1 2230. The sourcecell 2220 may transmit the new CHO request message to target cell 12230, for which the applicability check has failed, or may transmit theCHO cancellation message.

In operation 2213, the UE 2210 may store applicable candidate cellconfigurations, may perform measurement, and may evaluate CHO triggerconditions. For example, the UE 2210 may perform measurement for eachcandidate cell on the basis of the CHO configuration for each candidatecell (e.g., target cell 2 2240) for which an applicability check hasbeen successful, and may determine whether the CHO trigger condition foreach candidate cell is satisfied, on the basis of a measurement result.If one or more CHO trigger conditions are satisfied at a specific timepoint, the UE 2210 may select a target cell (e.g., target cell 2 2240)from among candidate cells, for which the CHO trigger condition issatisfied, and may perform a CHO to selected target cell 2 2240.

In operation 2215, the UE 2210 may transmit anRRCReconfigurationComplete message to the target cell 2230. If the CHOis successful, the UE 2210 may transmit a random access preamble, mayreceive an RAR, and may transmit the RRCReconfigurationComplete messageto target cell 2 2240 via message3 or message5.

FIG. 23 illustrates an example of a case of, if an applicability checkfor some candidate cell configurations among a plurality of CHOcandidate cell configurations has failed, performing RRE in the wirelesscommunication system according to various embodiments. In FIG. 23, a UE2310 may be the terminal 120, and operations of a source cell 2320,target cell 1 2330, and target cell 2 2340 may be performed by theelements of the base station 110.

Referring to FIG. 23, in operation 2301, the source cell 2320 maytransmit a CHO request to the target cell 2330. The source cell 2320 mayrequest a CHO from the target cell 2330 via a CHO request.

In operation 2303, the target cell 2330 may transmit a CHO request ACKto the source cell 2320. The target cell 2330 may transmit, to thesource cell 2320, the CHO request ACK message to accept the CHO request.

In operation 2305, the source cell 2320 may transmit an RRCreconfiguration message to the UE 2310. The RRC reconfiguration messagemay include a list of candidate cell configurations for a plurality ofcandidate cells, which includes a candidate cell configuration for acandidate cell (e.g., the target cell 2330), and each candidate cellconfiguration may include a candidate cell ID, a CHO configuration, anda CHO trigger condition for each candidate cell.

In operation 2307, the UE 2310 may determine whether each candidate cellconfiguration in the received list is applicable. In other words, the UE2310 may perform an applicability check for each candidate cellconfiguration. In FIG. 23, it is assumed that the applicability checkfor some of the candidate cell configurations of the received listfails. For example, it is assumed that the candidate cell configurationfor target cell 1 2330 is not applicable, and the candidate cellconfiguration for target cell 2 2340 is applicable.

In operation 2309, the UE 2310 may transmit, to the source cell 2320, anRRC message including CHO failure information that includes a candidatecell ID of a candidate cell (e.g., target cell 1 2230) to which thecandidate cell configuration is not applicable. As another embodiment,the RRC message may further include a candidate cell ID of a candidatecell (e.g., target cell 2 2340), for which the applicability check hasbeen successful.

In operation 2311, the source cell 2320 may transmit a CHO cancellationmessage or a new CHO request message to target cell 1 2330. The sourcecell 2320 may transmit the new CHO request message to target cell 12330, for which the applicability check has failed, or may transmit theCHO cancellation message.

In operation 2313, the UE 2310 may apply a current RRC configuration andmay perform an RRE procedure, or may transition to the RRC IDLE state.In other words, the UE 2310 may not apply the candidate cellconfiguration for a candidate cell (e.g., target cell 1 2330), for whichthe applicability check has failed, and may apply the RRC configurationcurrently being used by the UE 2310. If AS security is enabled, the UE2310 may perform RRE. If the AS security is not enabled, the UE 2310 maytransition to the RRC IDLE state.

FIG. 24 illustrates an example of a case of performing an applicabilitycheck for a candidate cell configuration for a candidate cell thatsatisfies a CHO trigger condition in the wireless communication systemaccording to various embodiments. In FIG. 24, a UE 2410 may be theterminal 120, and operations of a source cell 2420, target cell 1 2430,and target cell 2 2440 may be performed by the elements of the basestation 110.

Referring to FIG. 24, in operation 2401, the source cell 2420 maytransmit a CHO request to the target cell 2430. The source cell 2420 mayrequest a CHO from the target cell 2430 via a CHO request.

In operation 2403, the target cell 2430 may transmit a CHO request ACKto the source cell 2420. The target cell 2430 may transmit, to thesource cell 2420, the CHO request ACK message to accept the CHO request.

In operation 2405, the source cell 2420 may transmit an RRCreconfiguration message to the UE 2410. The RRC reconfiguration messagemay include a list of candidate cell configurations for a plurality ofcandidate cells, which includes a candidate cell configuration for acandidate cell (e.g., the target cell 2430), and each candidate cellconfiguration may include a candidate cell ID, a CHO configuration, anda CHO trigger condition for each candidate cell.

In operation 2407, the UE 2410 may store all candidate cellconfigurations, may perform measurement based on each candidate cellconfiguration, and may evaluate a CHO trigger condition for eachcandidate cell. In other words, the UE 2410 may store all candidate cellconfigurations of the received list, and may perform measurement basedon each candidate cell configuration.

In operation 2409, the UE 2410 may determine whether the CHO triggercondition for each candidate cell is satisfied. If one or more CHOtrigger conditions are satisfied at a specific time point, the UE 2410may select a target cell from among candidate cells, for which the CHOtrigger condition is satisfied, and may perform an applicability checkon the candidate cell configuration for the selected target cell. If theapplicability check fails, operations 2411 and 2413 may be performed. Inthis case, operation 2415 may be omitted. On the other hand, if theapplicability check succeeds, operation 2415 may be performed, andoperations 2411 and 2413 may be omitted.

In operation 2411, the UE 2410 may transmit an RRC message to the sourcecell 2420. The RRC message may include CHO failure information, and theCHO failure information may include a candidate cell ID of a candidatecell (e.g., target cell 1 2430), for which the candidate cellconfiguration is not applicable. The UE 2410 may transmit the RRCmessage in a state of applying a current RRC configuration.

In operation 2413, the source cell 2420 may transmit a CHO cancellationmessage or a new CHO request message to target cell 1 2430. The sourcecell 2420 may transmit the new CHO request message to target cell 12430, for which the applicability check has failed, or may transmit theCHO cancellation message.

As another example, in a case where the applicability check fails, if ASsecurity is enabled, the UE 2410 may performRRCConnectionRe-establishment (RRE), and if the AS security is notenabled, the UE 2410 may transition to the RRC IDLE state.

In operation 2415, the UE 2410 may transmit anRRCReconfigurationComplete message to target cell 2 2440. For example,the UE 2410 may perform a CHO to target cell 2 2440 on the basis of thecandidate cell configuration for target cell 2 2240, for which theapplicability check has been successful, and may transmit theRRCReconfigurationComplete message to target cell 2 2440.

FIG. 25 illustrates an example of a case of receiving CHO candidate cellconfigurations for a plurality of candidate cells together with areconfiguration related to a current serving cell in the wirelesscommunication system according to various embodiments. In FIG. 25, a UE2510 may be the terminal 120, and operations of a source cell 2520,target cell 1 2530, and target cell 2 2540 may be performed by theelements of the base station 110.

Referring to FIG. 25, in operation 2501, the source cell 2520 maytransmit a CHO request to target cell 1 2530. The source cell 2520 mayrequest a CHO from target cell 1 2530 via a CHO request.

In operation 2503, target cell 1 2530 may transmit a CHO request ACK tothe source cell 2520. Target cell 1 2530 may transmit, to the sourcecell 2520, the CHO request ACK message to accept the CHO request.

In operation 2505, the source cell 2520 may transmit an RRCreconfiguration message to the UE 2510. The RRC reconfiguration messagemay include reconfiguration information (hereinafter, it may be referredto as a serving cell reconfiguration) from a current serving cell (e.g.,2520) of the UE 2510, which is for reconfiguration of the configurationof the UE 2510, and a list of candidate cell configurations for aplurality of candidate cells, and each candidate cell configuration mayinclude a candidate cell ID, a CHO configuration, and a CHO triggercondition for each candidate cell.

In operation 2507, the UE 2510 may determine whether each of thecandidate cell configurations and the serving cell reconfiguration areapplicable. In other words, the UE 2510 may perform an applicabilitycheck for each of the candidate cell configurations and the serving cellreconfiguration. In various embodiments, if the applicability check forthe serving cell reconfiguration fails, regardless of whether theapplicability check for the candidate cell configurations is successful,the UE 2510 may apply configuration information for the current servingcell, and the UE 2510 may i) perform RRE (if AS security is enabled), orii) transition to the RRC IDLE state (if the AS security is notenabled). If the applicability check for the serving cellreconfiguration is successful, the UE 2510 may perform the applicabilitycheck for candidate cell configurations.

In operation 2509, the UE 2510 may transmit, to the source cell 2320, anRRC message including CHO failure information that includes a candidatecell ID of a candidate cell, to which the candidate cell configurationis not applicable. The UE 2510 may perform the applicability check forthe candidate cell configurations, and if there is a candidate cellconfiguration, for which the applicability check has failed, the UE 2510may transmit the RRC message, in which a reconfiguration failure type isindicated as a CHO configuration failure, to the source cell 2520,wherein the RRC message may include a candidate cell ID of a candidatecell, for which the applicability check has failed.

In operation 2511, the source cell 2520 may transmit a CHO cancellationmessage or a new CHO request message to target cell 1 2530. The sourcecell 2520 may transmit the new CHO request message to target cell 12530, for which the applicability check has failed, or may transmit theCHO cancellation message.

In operation 2513, the UE 2510 may store an applicable candidate cellconfiguration, may perform measurement based on the candidate cellconfiguration, and may evaluate a CHO trigger condition on the basis ofa measurement result. The UE 2510 may store the candidate cellconfiguration, for which the applicability check has been successful,may perform measurement for each candidate cell on the basis of the CHOconfiguration for each candidate cell, and may determine whether ameasurement result satisfies the CHO trigger condition for eachcandidate cell.

In operation 2515, the UE 2510 may transmit anRRCReconfigurationComplete message to target cell 2 2540. If one or moreCHO trigger conditions are satisfied at a specific time point, the UE2510 may select a target cell from among candidate cells, for which theCHO trigger condition is satisfied, and may perform a CHO to theselected target cell (e.g., target cell 2 2540). If the CHO issuccessful, the UE 2510 may transmit a random access preamble, mayreceive an RAR, and may transmit the RRCReconfigurationComplete messageto target cell 2 2540 via message3 or message5.

FIG. 26 illustrates a flowchart of a terminal in a case of receiving CHOcandidate cell configurations for a plurality of candidate cellstogether with a reconfiguration related to a current serving cell in thewireless communication system according to various embodiments. FIG. 26illustrates an operation method of the terminal 120.

Referring to FIG. 26, in operation 2601, the terminal may receive, froma source node, an RRC configuration message including a serving cellreconfiguration and a list of candidate cell configurations for multiplecandidate cells. Each candidate cell configuration may include acandidate cell ID, a CHO configuration, and a CHO trigger condition foreach candidate cell.

In operation 2603, the terminal may determine whether each of thereceived configurations is applicable. In other words, the terminal mayperform an applicability check for each of the multiple candidate cellconfigurations and the serving cell reconfiguration.

In operation 2605, the terminal may determine whether the serving cellreconfiguration is applicable. The terminal may perform an applicabilitycheck for the serving cell reconfiguration, and if the serving cellreconfiguration is not applicable, the terminal may perform operation2607. Alternatively, if the serving cell reconfiguration is applicable,operation 2609 may be performed.

In operation 2607, the terminal may apply a previous serving cellconfiguration and may perform RRE. If the applicability check for theserving cell reconfiguration fails, regardless of whether theapplicability check for the candidate cell configurations is successful,the terminal may apply an existing serving cell configuration, and theterminal may i) perform RRE (if AS security is enabled), or ii)transition to the RRC IDLE state (if the AS security is not enabled).

In operation 2609, the terminal may determine whether at least one ofthe candidate cell configurations is not applicable. If theapplicability check for the serving cell reconfiguration is successful,the terminal may perform an applicability check for each of thecandidate cell configurations. The terminal may identify a candidatecell configuration, for which an applicability check has beensuccessful, and a candidate cell configuration, for which anapplicability check has failed, and the terminal may i) performoperation 2611 for the candidate cell configuration for which theapplicability check has failed and, and ii) perform operation 2613 forthe candidate cell configuration for which the applicability check hasbeen successful.

In operation 2611, the terminal may transmit, to the source cell, theRRC message including CHO failure information that includes a candidatecell ID of a candidate cell, to which the candidate cell configurationis not applicable. The CHO failure information may include the candidatecell ID of the candidate cell for which the applicability check hasfailed. With respect to the candidate cell configuration for which theapplicability check has been successful, the terminal may store thecandidate cell configuration, may perform measurement based on thecandidate cell configuration, and may evaluate a CHO trigger conditionon the basis of a measurement result. The terminal may performmeasurement for each candidate cell on the basis of a CHO configurationfor each candidate cell, for which the applicability check has beensuccessful, and may determine whether the CHO trigger condition for eachcandidate cell is satisfied, on the basis of a measurement result.

In operation 2613, the terminal may store an applicable candidate cellconfiguration, may perform measurement based on the candidate cellconfiguration, and may evaluate the CHO trigger condition on the basisof a measurement result. The terminal may perform measurement for eachcandidate cell on the basis of a CHO configuration for each candidatecell, for which the applicability check has been successful, and maydetermine whether the CHO trigger condition for each candidate cell issatisfied, on the basis of a measurement result. If one or more triggerconditions are satisfied at a specific time point, the terminal mayselect a target cell from among candidate cells, for which the CHOtrigger condition is satisfied, and may perform a CHO to the selectedtarget cell. If the CHO is successful, the terminal may transmit arandom access preamble, may receive an RAR, and may transmit theRRCReconfigurationComplete message to target cell 2 2540 via message3 ormessage5.

The scope of protection is defined by the appended independent claims.Further features are specified by the appended dependent claims. Exampleimplementations can be realized comprising one or more features of anyclaim taken jointly and severally in any and all permutations.

The examples described in this disclosure include non-limiting exampleimplementations of components corresponding to one or more featuresspecified by the appended independent claims and these features (ortheir corresponding components) either individually or in combinationmay contribute to ameliorating one or more technical problems deducibleby the skilled person from this disclosure.

Furthermore, one or more selected component of any one example describedin this disclosure may be combined with one or more selected componentof any other one or more example described in this disclosure, oralternatively may be combined with features of an appended independentclaim to form a further alternative example.

Further example implementations can be realized comprising one or morecomponents of any herein described implementation taken jointly andseverally in any and all permutations. Yet further exampleimplementations may also be realized by combining features of one ormore of the appended claims with one or more selected components of anyexample implementation described herein.

In forming such further example implementations, some components of anyexample implementation described in this disclosure may be omitted. Theone or more components that may be omitted are those components that theskilled person would directly and unambiguously recognize as being not,as such, indispensable for the function of the present technique in thelight of a technical problem discernible from this disclosure. Theskilled person would recognize that replacement or removal of suchomitted components does not require modification of other components orfeatures of the further alternative example to compensate for thechange. Thus further example implementations may be included, accordingto the present technique, even if the selected combination of featuresand/or components is not specifically recited in this disclosure.

Two or more physically distinct components in any described exampleimplementation of this disclosure may alternatively be integrated into asingle component where possible, provided that the same function isperformed by the single component thus formed. Conversely, a singlecomponent of any example implementation described in this disclosure mayalternatively be implemented as two or more distinct components toachieve the same function, where appropriate.

Methods disclosed in the claims and/or methods according to variousembodiments described in the specification of the disclosure may beimplemented by hardware, software, or a combination of hardware andsoftware.

When the methods are implemented by software, a computer-readablestorage medium for storing one or more programs (software modules) maybe provided. The one or more programs stored in the computer-readablestorage medium may be configured for execution by one or more processorswithin the electronic device. The at least one program may includeinstructions that cause the electronic device to perform the methodsaccording to various embodiments of the disclosure as defined by theappended claims and/or disclosed herein.

The programs (software modules or software) may be stored innon-volatile memories including a random access memory and a flashmemory, a read only memory (ROM), an electrically erasable programmableread only memory (EEPROM), a magnetic disc storage device, a compactdisc-ROM (CD-ROM), digital versatile discs (DVDs), or other type opticalstorage devices, or a magnetic cassette. Alternatively, any combinationof some or all of them may form a memory in which the program is stored.Further, a plurality of such memories may be included in the electronicdevice.

In addition, the programs may be stored in an attachable storage devicewhich may access the electronic device through communication networkssuch as the Internet, Intranet, Local Area Network (LAN), Wide LAN(WLAN), and Storage Area Network (SAN) or a combination thereof. Such astorage device may access the electronic device via an external port.Further, a separate storage device on the communication network mayaccess a portable electronic device.

In the above-described detailed embodiments of the disclosure, anelement included in the disclosure is expressed in the singular or theplural according to presented detailed embodiments. However, thesingular form or plural form is selected appropriately to the presentedsituation for the convenience of description, and the disclosure is notlimited by elements expressed in the singular or the plural. Therefore,either an element expressed in the plural may also include a singleelement or an element expressed in the singular may also includemultiple elements.

Although specific embodiments have been described in the detaileddescription of the disclosure, modifications and changes may be madethereto without departing from the scope of the disclosure. Therefore,the scope of the disclosure should not be defined as being limited tothe embodiments, but should be defined by the appended claims andequivalents thereof.

Although the present disclosure has been described with variousembodiments, various changes and modifications may be suggested to oneskilled in the art. It is intended that the present disclosure encompasssuch changes and modifications as fall within the scope of the appendedclaims.

What is claimed is:
 1. A method performed by a user equipment (UE) in awireless communication system, the method comprising: receiving, from abase station, a radio resource control (RRC) reconfiguration messageincluding conditional configuration information, wherein the conditionalconfiguration information includes: identification information for acandidate cell; and a configuration of the candidate cell; andperforming one or more operations for a conditional handover based onthe RRC reconfiguration message.
 2. The method of claim 1, wherein theconditional configuration information further includes information on acondition for triggering an execution of the configuration of thecandidate cell, and wherein the performing of the one or more operationsfor the conditional handover comprises evaluating the condition.
 3. Themethod of claim 2, wherein the performing of the one or more operationsfor the conditional handover comprises: based on identifying that thecondition is met based on a measurement result, applying the conditionalconfiguration.
 4. The method of claim 1, further comprising: identifyingwhether the identification information for the candidate cell exists ina list stored in the UE; and if the identification information for thecandidate cell does not exist in the list stored in the UE, storing theconditional configuration information.
 5. The method of claim 4, furthercomprising: if the identification information for the candidate cellexists in the list stored in the UE, replacing one configuration of thecandidate cell stored in the UE with the received configuration of thecandidate cell.
 6. The method of claim 4, further comprising: if theidentification information for the candidate cell exists in the liststored in the UE, replacing one condition of the candidate cell storedin the UE with a condition for triggering an execution of theconfiguration of the candidate cell, wherein the conditionalconfiguration information further includes information on the condition.7. The method of claim 1, further comprising: receiving, from the basestation, an RRC reconfiguration message including information on arelease list including identification information for another candidatecell; and if the identification information for another candidate cellexists in the list stored in the UE, releasing a conditionalconfiguration corresponding to the identification information foranother candidate cell.
 8. The method of claim 1, wherein the RRCreconfiguration message includes an addition/modification list for oneor more conditional configuration information, and wherein theaddition/modification list includes the conditional configurationinformation.
 9. A user equipment (UE) in a wireless communicationsystem, comprising: at least one transceiver; and at least one processorconfigured to: receive, from a base station via the at least onetransceiver, a radio resource control (RRC) reconfiguration messageincluding conditional configuration information, wherein the conditionalconfiguration information includes: identification information for acandidate cell; and a configuration of the candidate cell; and performone or more operations for a conditional handover based on the RRCreconfiguration message.
 10. The UE of claim 9, wherein the conditionalconfiguration information further includes information on a conditionfor triggering an execution of the configuration of the candidate cell,and wherein the performing of the one or more operations for theconditional handover comprises evaluating the condition.
 11. The UE ofclaim 10, wherein the at least one processor is, in order to perform theone or more operations for the conditional handover, configured to:based on identifying that the condition is met based on a measurementresult, apply the conditional configuration.
 12. The UE of claim 9,wherein the at least one processor is further configured to: identifywhether the identification information for the candidate cell exists ina list stored in the UE; and if the identification information for thecandidate cell does not exist in the list stored in the UE, store theconditional configuration information.
 13. The UE of claim 12, whereinthe at least one processor is further configured to: if theidentification information for the candidate cell exists in the liststored in the UE, replace one configuration of the candidate cell storedin the UE with the received configuration of the candidate cell.
 14. TheUE of claim 12, wherein the at least one processor is further configuredto: if the identification information for the candidate cell exists inthe list stored in the UE, replace one condition of the candidate cellstored in the UE with a condition for triggering an execution of theconfiguration of the candidate cell, wherein the conditionalconfiguration information further includes information on the condition.15. The UE of claim 9, wherein the at least one processor is furtherconfigured to: receive, from the base station via the at least onetransceiver, an RRC reconfiguration message including information on arelease list including identification information for another candidatecell; and if the identification information for another candidate cellexists in the list stored in the UE, release a conditional configurationcorresponding to the identification information for another candidatecell.
 16. The UE of claim 9, wherein the RRC reconfiguration messageincludes an addition/modification list for one or more conditionalconfiguration information, and wherein the addition/modification listincludes the conditional configuration information.
 17. A base stationin a wireless communication system, comprising: at least onetransceiver; and at least one processor configured to: generate a radioresource control (RRC) reconfiguration message including conditionalconfiguration information, wherein the conditional configurationinformation includes: identification information for a candidate cell;and a configuration of the candidate cell; and transmit, to a userequipment (UE) via the at least one transceiver, a radio resourcecontrol (RRC) reconfiguration message for a conditional handover. 18.The base station of claim 17, wherein the conditional configurationinformation further includes information on a condition for triggeringan execution of the configuration of the candidate cell.
 19. The basestation of claim 17, wherein the at least one processor is, beforegenerating the RRC reconfiguration message, further configured to:transmit, to a target base station providing the candidate cell via theat least one transceiver, a handover request message, and receive, fromthe target base station via the at least one transceiver, a handoverrequest acknowledge message including the configuration of the candidatecell.
 20. The base station of claim 17, wherein the at least oneprocessor is further configured to: transmit, to the UE via the at leastone transceiver, an RRC reconfiguration message including information ona release list including identification information for anothercandidate cell, wherein a conditional configuration corresponding to theidentification information for another candidate cell is released.